Provide find module for OPM Parser library

Searches for headers and objects of the library as well as finding
the prerequisites (Boost and CJSON) necessary to link a program.
Define uppercase variant when testing for existence

CMake will do some uppercasing of its own (defining OPM-PARSER_FOUND)
so it works best if we specify the correct uppercase version and sets
the lowercase afterwards.
Include standard CMake module to get error handling
Merge pull request #35 from rolk/035_cmake

Provide find module for OPM Parser library