Fix bug that caused coordinates such as -00:00:10 to end up being positive. The issue is that while float('-00') returns a negative zero, int('-00') does not, so we need to take care of always using float rather than int when converting degrees or hours to numerical values.
Fixed typo
Merge pull request #875 from astrofrog/fix-issue-875

dms declinations with -00 not treated correctly
Added changelog entries for #867 and #875
Update changelog post 0.2.1 release