Pyfasta

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* restore python2.5 compatiblity.
* CLI: add ability to exclude sequence from extract
* CLI: allow spliting based on header.

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* include this file in the tar ball (thanks wen h.)

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* separate out backends into records.py

* use nosetests (python setup.py nosetests)

* add a TCRecord backend for next-gen sequencing availabe if tc is (easy-)installed.

* improve test coverage.