Tokenstream

Fix
* Make it possible to emit errors from tokens ([`b97ab2d`](https://github.com/vberlier/tokenstream/commit/b97ab2d4913c2f0410251ab0cbb817f5082a61df))

Feature
* Add stream.alternative(bool) ([`3adef70`](https://github.com/vberlier/tokenstream/commit/3adef707670c8a1cb00cca3c3d5174c1db4f0d0b))

Fix
* Don't capture newlines in whitespace tokens ([`d17783e`](https://github.com/vberlier/tokenstream/commit/d17783eb3f13ce4eb5c18ee36eb3bc92434f10a9))

Fix
* Handle pattern explanation with no pattern ([`1de098b`](https://github.com/vberlier/tokenstream/commit/1de098b069315cb56670739238f133020fd5fd3c))

Feature
* Add arbitrary user data ([`105553f`](https://github.com/vberlier/tokenstream/commit/105553f073a03ccee25eb2330f6d69459279802b))

Feature
* Add alternative method and choose method ([`0794172`](https://github.com/vberlier/tokenstream/commit/0794172e558722bceb3353af609562520185967c))

Fix
* Swallow syntax errors when checkpoint is not committed yet ([`54e77ef`](https://github.com/vberlier/tokenstream/commit/54e77ef25033cd0a19ec7d716deb855ac389d0d7))
* Don't raise UnexpectedEOF if peek_until without patterns ([`bcee95a`](https://github.com/vberlier/tokenstream/commit/bcee95af5d25344f29f9de43c3b6ed2c7d1e2c27))