Clean up feature comparison operators

[standage]

This update cleans up comparison operators for Feature objects. I had also planned on implementing __eq__ and __hash__ operators (see below), but this causes issues during traversal with duplicate features (such as exons defined multiple times; related to #30).

    def __eq__(self, other):
        if not isinstance(other, Feature):
            return False
        if self.seqid != other.seqid or self._range != other._range:
            return False
        if self.type != other.type or self.source != other.source:
            return False
        return True

    def __hash__(self):
        return hash((self.seqid, self.range, self.type, self.source))

• Full test coverage? Any additional tests that could easily be added?
• API documentation up-to-date? Docstring examples?
• Is the CHANGELOG up-to-date?

[codecov-io]

Codecov Report

Merging #67 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #67   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          18     18           
  Lines        1091   1073   -18     
  Branches      254    244   -10     
=====================================
- Hits         1091   1073   -18

Impacted Files	Coverage Δ
tag/range.py	100% <100%> (ø)	⬆️
tag/feature.py	100% <100%> (ø)	⬆️

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