1.2.0 release

[grinner]

• Threadsafe changes made to thal.c resulting in new thalflex.c and thalflex.h and thalflexsignatures.h.
• Threadsafe changes made to libprimer3.c resulting in new libprimer3flex.c and ibprimer3flex.c.h.
• libprimer3.seq_args datatype is now renamed to libprimer3.seq_args_t
• test_threadsafe.py add and nogil instituted for calls to thal() and seqtm() added run_design and calc_heterodimer threadsafe tests
• ThermoAnalysis class no longer needs to be a Singleton so this was removed as a parent class
• p3helpers.pyx houses new sequence and design helper functions
• setup.py package_data and MANIFEST.in to assist with future builds from tar.gz (conda)