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/regexp.go

@@ -6,6 +6,7 @@ import (
 	"regexp"
 	"strings"
 	"sync"
+	"time"
 	"unicode/utf8"
 
 	"github.com/dlclark/regexp2"
@@ -160,6 +161,14 @@ func Tokenise(lexer Lexer, options *TokeniseOptions, text string) ([]Token, erro
 // Rules maps from state to a sequence of Rules.
 type Rules map[string][]Rule
 
+// Rename clones rules then a rule.
+func (r Rules) Rename(old, new string) Rules {
+	r = r.Clone()
+	r[new] = r[old]
+	delete(r, old)
+	return r
+}
+
 // Clone returns a clone of the Rules.
 func (r Rules) Clone() Rules {
 	out := map[string][]Rule{}
@@ -170,6 +179,15 @@ func (r Rules) Clone() Rules {
 	return out
 }
 
+// Merge creates a clone of "r" then merges "rules" into the clone.
+func (r Rules) Merge(rules Rules) Rules {
+	out := r.Clone()
+	for k, v := range rules.Clone() {
+		out[k] = v
+	}
+	return out
+}
+
 // MustNewLexer creates a new Lexer or panics.
 func MustNewLexer(config *Config, rules Rules) *RegexLexer {
 	lexer, err := NewLexer(config, rules)
@@ -376,6 +394,7 @@ func (r *RegexLexer) maybeCompile() (err error) {
 				if err != nil {
 					return fmt.Errorf("failed to compile rule %s.%d: %s", state, i, err)
 				}
+				rule.Regexp.MatchTimeout = time.Millisecond * 250
 			}
 		}
 	}