diff: fix patience diff
diff: DiffString

use low-level string optimisations to reduce memory consumption and gc
share char[] buffer between substrings and try to reuse it on concatenations
diff: unify LineTokenizers
diff: rewrite DiffFragment
diff: fix typo
diff: do not create LineSeparator string every time
Github: enable twofactor authorization

wrap immutable GithubAuthData into mutable GithubAuthDataHolder with synchronized access
Github: do not rethrow exception twice
Github: rewrite AuthDataHolder

encapsulate lock-critical parts
Github: codereview
Github: AtomicRef -> Ref
Github: inspection warnings
Github: do not provide Login/Password AuthData to Git on TwoFactor enabled

Git doesn't work with it and handles error poorly
diff: fix patience diff
Merge branch 'diff-string'
Merge branch 'two-factor-auth'