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
Force travis to use sphinx v1.1.3

Closes #934
Merge pull request #875 from astrofrog/fix-issue-875

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