Added qiime.simsam.create_replicated_mapping_file.

Also added unit tests.
Added docstring.
Added -m/--mapping_fp option to simsam.py.
Existing unit tests now pass.
Added mention to ChangeLog.

Fixes #784.
Added default to -m/--mapping_fp option help text.
Merge pull request #786 from jrrideout/issue-784

Added -m/--mapping_fp option to simsam.py
ported code from a fork of my gregcaporaso/microbiogeo repo

never actually merged that fork into microbiogeo as it makes more sense for this code to be in QIIME
added myself to the credits
changed import mechanism
fixed error introduced in my last commit
updated to hook simsam_range up to the command line
updated tests to use new output file names
added usage example
updated documentation and function name
added ability to override the 'basename' for the output files
updated script to override table and map basenames
added failing tests - issue caught by @jrridout
fixed typo
fixed bug in formatting of mapping file