grep: move match and diff logic to new module
commands.grep() has lots of functions and classes. Let's split it into
reusable components so we can leverage them to implement a revset predicate
for 'hg grep --diff'. I want to do 'hg log -r "diff(pattern)"'.
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2