[MAT-425] patches to enable izy linkage and tests

This adds in the ability to link against OG-Izy. It adds an izy
namespace and then demonstrates the pattern needed to add a
single function binding from izy to the namespace and tests it.
[MAT-425] add izy yaml info to top level verinfo yaml

This adds the ability to accept multiple subprojects in
verinfo.py. It then adds the necessary wiring to include the
buildinfo yaml from izy into the OG-Maths master yaml.
[MAT-425] Respond to review comments.

This updates verinfo.py to report on the failed subproject name.
It also bumps INSTALL.md to reflect the inclusion of OG-Izy.
Merge pull request #122 from OpenGamma/MAT-425

Mat 425 add in OG-Izy wiring.