Upgrades to vexcl.m4

Test for boost before vexcl (vexcl headers require boost headers in
the include path, and I was just getting that by luck before)

Other reorganization and improved error handling.
Compilation bugfix
Create compute_mole_sources intermediary since we may want
things in moles and not mass. mass_sources internally calls
this now.
Starting to add derivative version of compute_mole_sources.
Finished up mole_sources deriv routine. mass_sources now
internally calls this.
Merge pull request #6 from pbauman/compute_mole_sources

Add compute_mole_sources, etc. to KineticsEvaluator
Last kinetics tests added
!!!
In certain conditions, van't hoff kinetics do not pass the test, here's
an exemple:
A = 1.135e36 * 1e-6;
eta = -5.246;
Ea = 1704.8 / 1.9858775;
D = -4e-2;
This will give difficult values for the Van't Hoff equation:
k = A * pow(T,eta) * exp(-Ea/T + D * T);
Small changes to documentations