Tokenstream

Fix
* Handle non SourceLocation end_location in set_location ([`f16b378`](https://github.com/vberlier/tokenstream/commit/f16b378fbdc52942bcf14a8d4b41d34158d867d7))

Feature
* Move SourceLocation into its own module ([`95aabae`](https://github.com/vberlier/tokenstream/commit/95aabae6058bb3c13bbd4f15a372d480f94a22b2))

Breaking
* remove InvalidSyntax.set_location in favor of the general-purpose setlocation function ([`95aabae`](https://github.com/vberlier/tokenstream/commit/95aabae6058bb3c13bbd4f15a372d480f94a22b2))

Fix
* Combine unexpected token patterns when using the choose() method ([`b8665e8`](https://github.com/vberlier/tokenstream/commit/b8665e8b10e451467e2dae1659e9c999213aa348))

Fix
* Tweak pattern explanation when there are a lot of token types ([`0a9e007`](https://github.com/vberlier/tokenstream/commit/0a9e007ea77095e040f87c9c0c61539b3245e7a1))

Fix
* Properly restore previous regex when syntax changes ([`aeae860`](https://github.com/vberlier/tokenstream/commit/aeae860707149ec6bd1e2d730dd613cf097c231d))

Fix
* Raise IndexError for negative indices for current and previous tokens ([`7b5010b`](https://github.com/vberlier/tokenstream/commit/7b5010bfb801ee1e72d1a16a039aa2ff9ab7d1b9))