DOC : make use of autolink

 - will auto-link if a word in `` is a class or function
DOC : added explanatory comments to autolink
DOC : added style re one-line if statements

 - Added prose to docs regarding style.
MNT: Check to see if this fixes the py3 travis bug
Merge pull request #90 from ericdill/py3_oddness

MNT: Check to see if this fixes the py3 travis bug

Merging my own PR just so travis will stop failing
Update README.md
Merge pull request #73 from tacaswell/doc_tweak

DOC : make use of autolink
Merge pull request #88 from tacaswell/if_doc

DOC : added style re one-line if statements
init of data structure for xrf fit
add calculations of cs, line_energy, jumpfactor
add element data file to save data as dict
add license
add more docstring
MNT : PEP8 white-space fixes
MNT : re-factored back end data structures

 - turned OTHER_VAL into a dict keyed on both
   the symbol and Z
 - simplified the data look up in Element
MNT : simplified handling of energy

  - just try to cast to float.  Let python deal with the conversion.
    If it can't be done it will raise an exception.
MNT : use np.nan for missing values

I am interpreting 0 in the density of Fm as meaning 'not enough of this
has ever been made'.  Use np.nan so that computations using this value
will fail (yield nan), rather that silently, but incorrectly, work.
ENH : make any cases work for element symbols

force all string inputs to be lowercase when keying the
dictionary.
correct name and add more docstring
add unit