Fixes #6735

Since #6273 was merged, we now have access to proper context metas
always. Update SHA generated links to use these instead of urlPrefix.

Update tests as well.

Fixes #4536.

* Improve issue autolinks

Update autolinks to match what github does here:

Issue in same repo: #1
Issue in different repo: org/repo#1

Fixes #6264

* Use setting.AppURL when parsing URL

Using setting.AppURL here is a more reliable way of parsing the current
URL and what other functions in this file seem to use.

* Make ComposeMetas always return a valid context

* Add per repository markdown renderers for better context

* Update for use of context metas

Now that we include the user and repo name inside context metas, update
various code and tests for this new logic

* Use stricter boundaries for auto-link detection

Currently autolinks use \W for boundary detection which creates many
situations of inserting links into places they don't belong (paths,
URLs, UUIDs, etc...)

This fixes that by replacing \W and only allowing these matches to touch
an open paren or bracket (matching what seems to be Github behavior) in
addition to whitespace and start of line. Similar for ending boundary as
well.

Fixes #6149
(and probably others)

* Update test

Replace incorrect test with a value that is a valid username, based on:

"Username should contain only alphanumeric, dash ('-'), underscore ('_')
and dot ('.') characters."

* Also allow for period at the end

Matching Github behavior

* Fix email regex to work properly with specificed boundaries

Create a specific capture group for email address and then use
FindStringSubmatchIndex to allow for non-matching patterns as
boundaries.

* Add Tests

Add tests for new behavior -- including tests for email addresses which
were absent before.

This improves the SHA1 link detection to not pick up extraneous
non-whitespace characters at the end of the URL. The '.' is a special
case handled in code itself because of missing regexp lookahead
support.

Regex test cases: https://regex101.com/r/xUMlqh/3

Make sure Processors that work on full links are run first so that
something matching another pattern doesn't alter a link before we get to
it, for example:

 https://stackoverflow.com/questions/2896191/what-is-go-used-fore

Fixes #4813

* Migrate to go modules

* make vendor

* Update mvdan.cc/xurls

* make vendor

* Update code.gitea.io/git

* make fmt-check

* Update github.com/go-sql-driver/mysql

* make vendor

* Replace linkRegex with xurls library

Rather than maintaining a complicated regex to match URLs for
autolinking, gitea can use this existing go library that takes care of
the matching with very little code change to gitea itself. After
spending a while trying to find the perfect regex for all cases this library
still works better as it is more flexible than a single regex ever will be.

This will also fix the following issues: #5844 #3095 #3381

This passes all our current tests and I've added new ones mentioned in
those issues as well.

* Use xurls.StrictMatchingScheme instead of xurls.Strict

This is much faster and we only care about https? links to preserve
existing behavior.

The visitLinksForShortLinks feature would look inside of an <a> tag and
run shortLinkProcessorFull on any text, which attempts to create links
out of potential 'short links' like [[test]] [[link|example]] etc...
This makes no sense because you can't have nested links within an <a>
tag. Specifically, the html5 standard says <a> tags can't include
interactive content if they contain the href attribute:

 http://w3c.github.io/html/single-page.html#the-a-element

And also defines an <a> element with a href attribute as interactive:

 http://w3c.github.io/html/single-page.html#interactive-content

Therefore you can't really put a link inside of another link. In
practice none of this works anyways since browsers won't render it, it
would probably be broken if they tried, and it is causing a bug
(#4946). No current tests rely on this behavior either.

This removes the feature and also explicitly excludes the
current visitNodeForShortLinks from looking in <a> tags.

Modify the current linkRegex to require http|https which appears to be
the intended behavior based on the comments. Right now, it also matches
anything starting with www as well. Also add testing for linkRegex

* Get rid of autolink

* autolink in markdown

* Replace email addresses with mailto links

* better handling of links

* Remove autolink.js from footer

* Refactor entire html.go

* fix some bugs

* Make tests green, move what we can to html_internal_test, various other changes to processor logic

* Make markdown tests work again

This is just a description to allow me to force push in order to restart
the drone build.

* Fix failing markdown tests in routers/api/v1/misc

* Add license headers, log errors, future-proof <body>

* fix formatting

* Populate URL field of API commits

* fix orgmode_test

* Allow square brackets in external issue patterns

* Added false test cases for checklist elements

* Fix issue link rendering in commit messages

* Update page.tmpl

* No links for parens

* remove comment

* restructure markup & markdown to prepare for multiple markup languages support

* adjust some functions between markdown and markup

* fix tests

* improve the comments