Backrefs

Jan 22, 2018

- **FIX**: Bregex purge was calling Re's purge instead of Regex's purge.

Jan 21, 2018

- **FIX**: Do not accidentally `\.` as a group in replace strings (don't use `isdigit` string method).
- **FIX**: Group names can start with `_` in replace strings.
- **FIX**: Do not rely on Re for parsing string.
- **FIX**: Match behavior in `\g<group>` parsing better.
- **FIX**: Raise some exceptions in a few places we weren't.

Jan 20, 2018

- **NEW**: Added new `compile` function that returns a pattern object that feels like Re's and Regex's pattern object.
- **NEW**: Add some caching of search and replace patterns.
- **NEW**: Completely refactored algorithm for search and replace pattern augmentation.
- **NEW**: Add support for `\e` for escape character `\x1b` in both Re and Regex.
- **NEW**: Add support for `\R` for generic newlines in the Regex module (Regex only).
- **NEW**: Support Unicode property form `\pP` and `\PP`.
- **NEW**: Add support for properly handling per group, scoped verbose flags in the preprocess step (Regex).
- **NEW**: Handle `(?comments)` properly in the preprocess step.
- **NEW**: Add support for `\N` in byte strings (characters out of range won't be included).
- **NEW**: Add support for `\p` and `\P` in byte strings (characters out of range won't be included).
- **NEW**: Add support for `\<` and `\>` word boundary escapes.
- **FIX**: Missing block properties on narrow systems when the property starts beyond the narrow limit.
- **FIX**: Fix issue where an invalid general category could sometimes pass and return no characters.
- **FIX**: Fix `\Q...\E` behavior so it is applied first as a separate step. No longer avoids `\Q...\E` in things like character groups or comments.
- **FIX**: Flag related parsing issues in Regex and Re Python 3.6+.

Release candidate 1 for 2.3.0 ... will actually be released as 3.0.