Remove Libs: content from pkg-config template

I missed doing this when issue #27 was fixed.
Merge pull request #34 from RhysU/fix_pc_in

Remove Libs: content from pkg-config template
Make get_antioch_version inline

Also makes antioch_version_stdout inline to avoid -Wunused warnings.
Reorders methods to remove the need for forward declarations.
Closes #35 on private testing.
Merge pull request #36 from RhysU/static_version_method

Make get_antioch_version static
Any Kooij with a beta = 0 is converted into Arrhenius,

tests is added in parsing_xml.C and its input file
This warning is not from deprecated code...
Merge pull request #39 from SylvainPlessis/Kooij-Arr

Fix issue #38
Ridiculous bug I've introduced...
Here's the code as it should have been all along...
Forgotten Tref() method definition in VantHoffRate
Merge pull request #43 from SylvainPlessis/kin_Tref

Forgotten Tref() method definition in VantHoffRate, rebased and merged