Add a travis configuration file.

It builds the library and examples for mode=small, hse=25000000,
and three of the supported MCUs.
Add travis badge for andysworkshop.
edited hse values to 8MHz for most, 25 for the ethernet f107
Merge branch 'mikepurvis-travis-config'
Merge branch 'master' of github.com:andysworkshop/stm32plus