Xml parser

[SylvainPlessis]

Here is the PR related to issue #173.

It has all the discussed features:

• if verbose, it says which rate constant is the low pressure and which is the high pressure limit
• within a falloff environment, no other value than k0 is allowed for a name attribute
• within a falloff environment, no more than one name attribute is allowed
• doxygen docs have been updated

Two expected failures tests have been added to test for these two new restrictions, the existing test have been somewhat expanded, meaning some name="k0" have been put in the first rate constant's block to test for this configuration.

The XFAIL tests are clones of the normal test, with one reaction containing one feature that Antioch now find to be offensive.

[SylvainPlessis]

On this, gentlemen, I'm heading for my bed.

See ya!

[pbauman]

Closed in favor of #175. Thanks @SylvainPlessis!