add support for building with cmake

[aivazis]

now that pyre builds with cmake, we should add cmake support in altar and retire the default build system

[lijun99]

I tried cmake on Linux and it worked perfectly!

1. I will try Mac/Anaconda when I get access to a mac;
2. I will follow your example to write a cmake file for the seismic model as well as for cuda extensions;
3. I can also take care of the installation how-to.

[lijun99]

I have added cmake support to cuda extensions in pyre and altar as well. All things go well. The only hassle is that when using enable_language(CUDA) instead of FindCUDA, it does not seem to work inside a function and has to be put under PARENT_SCOPE. I will do more tests and write a guide next week. Mac/Anaconda also works well. Shall we write a setup.py to make the installation step even simpler?