allow mbed target to build by defining luaopen_dummy earlier
 Committer: Omnima Dev Team  <info@omnima.co.uk>
 new file:   boards/known/omniexp.lua
Merge pull request #34 from omnima/master

 Committer: Omnima Dev Team  <info@omnima.co.uk>
Move DAC functionality into stm32f4 specific module (stm32f4.sa_dac).
Merge branch 'master' into mb-stm32f4-dac