…ompare/v0.6.14...v0.6.15)

**Closed issues:**
- Incorrect planar_hull (#253)

**Merged pull requests:**
- Fix variable name in error message (#252) (@schillic)
- More robust planarhull for colinear points (#254) (@blegat)
- Replace _promote_type by MutableArithmetics promotion (#255) (@blegat)