Add RSA output

Changes:

• CLI options --rsa and --rsa-file can be used to output RSA files similar to those of NACCESS. RSA is mainly intended to be useful as a CLI setting, the RSA API is still to be considered experimental. Since there might be need for more functionality before it stabilizes. A file format for RSA reference values might be added in the future, for example.
• The library ships with AXA tripeptides that can be used to calculate new RSA reference SASA values, and a simple Perl script that performs this calculation and outputs C code for the combined reference values for all 20 residues.
• Options -O and --radius-from-occupancy were added to allow using the occupancy values in the input file as atomic radii. This can be useful for on the fly changes, or if individual atoms need special treatment.
• An NACCESS configuration is now also stored statically in the library, this allows the CLI to produce RSA output with verified consistency between atomic radii and SASA reference values. This is access through the option --radii=naccess (or --radii=protor).
• Travis and Coveralls testing have been added to the configuration