Support build & install via CMake#6

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FaultyRAM wants to merge 2 commits intoshmup:masterfrom

FaultyRAM:cmake

Commits on May 8, 2015

added CMakeLists.txt (placeholder proj. ver., docs not built)
FaultyRAM
committed

Commits on May 9, 2015

Build documentation and install the output, if nroff is available
FaultyRAM
committed