relax SVN archive

Added the missing import of relax_io.strip.

Fixed the path in the unit test for reading a protein sequence.

Updated the extract_data() for the new relax design (converted from a class method to a function).

Started to implement the read, sequence_exists, and valid_sequence functions.

Small fix for RelaxInvalidSeqError.

Added a new RelaxError for invalid sequence data.

Wrote a unit test for the writing of an amino acid sequence to file.

Added unit tests for all arguments of the sequence.write() user function.

Updated the sequence.write() user function for the new relax design.

Fixed all user function arg unit tests to use the new DATA_TYPES module array.