Trying to fix issue 524
refactoring code resolves #495
Fixed issue #502
refactoring code resolves #495
removing comments resolves #495
fixed descr --> description
adding accidentally removed prints back in
Moves khmer exception classes to their own file and defines new base class for all
exceptions.
code review comments
updated ChangeLog
Merge pull request #551 from jstapleton/fix/524

Fix/524
Fixed issue #502
All exceptions defined in khmer are derived class from khmer::khmer_exception,
including khmer::khmer_file_exception.
autopep8 formatting
Merge branch 'fix/502' of github.com:RodPic/khmer into RodPic-fix/502
Merge branch 'RodPic-fix/502'
updated changelog
modified tests to use less memory
Should fix pip2 / make test issues
Should fix pip2 / make test issues