Fixes to CMakeLists

[Flow-It]

The usage of CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_BINARY_DIR is encouraged over the use of CMAKE_SOURCE_DIR and CMAKE_BINARY_DIR respectivly. In addition, bump the required minimum version to 3.0 to avoid warnings about the old version 2. CMAKE_MODULE_PATH is not a variable to hold a specific directory. Instead, add the cmake directory which holds the hyperscan-specific CMake modules to CMAKE_MODULE_PATH and replace its usages. include() directives can now simply use the filename (it is picked up without the .cmake extension, because we added the directory to the module path). The remaining usages where the exact directory was referenced are replaced with $PROJECT_SOURCE_DIR/cmake, although one could probably even use a new variable for that directory.