Detect markdown line width, resolve relative URLs (#332)

~~this is semi-blocked by https://github.com/charmbracelet/glamour/pull/96, but behaviour isn't really worse than the previous behaviour (most links work, some are still broken)~~

#### testcase for link resolver
```
tea pr 332
tea checkout 332 && make install && tea pr 332
```

- [rel](./332)
- [abs](/gitea/tea/pulls/332)
- [full](https://gitea.com/gitea/tea/pulls/332)

Co-authored-by: Norwin Roosen <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/332
Reviewed-by: 6543 <6543@obermui.de>
Reviewed-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

vendor/github.com/alecthomas/chroma/lexers/b/bash.go

@@ -36,7 +36,7 @@ var Bash = internal.Register(MustNewLexer(
 			{`\b(if|fi|else|while|do|done|for|then|return|function|case|select|continue|until|esac|elif)(\s*)\b`, ByGroups(Keyword, Text), nil},
 			{"\\b(alias|bg|bind|break|builtin|caller|cd|command|compgen|complete|declare|dirs|disown|echo|enable|eval|exec|exit|export|false|fc|fg|getopts|hash|help|history|jobs|kill|let|local|logout|popd|printf|pushd|pwd|read|readonly|set|shift|shopt|source|suspend|test|time|times|trap|true|type|typeset|ulimit|umask|unalias|unset|wait)(?=[\\s)`])", NameBuiltin, nil},
 			{`\A#!.+\n`, CommentPreproc, nil},
-			{`#.*\S`, CommentSingle, nil},
+			{`#.*(\S|$)`, CommentSingle, nil},
 			{`\\[\w\W]`, LiteralStringEscape, nil},
 			{`(\b\w+)(\s*)(\+?=)`, ByGroups(NameVariable, Text, Operator), nil},
 			{`[\[\]{}()=]`, Operator, nil},