Builds should not be forced to output files to the source directory

[inkychris]

The customisation of output directories in the top-level CMakeLists.txt file makes it impossible to control where targets in this project are built. These customisations should be removed/guarded with an option that allows the user to decide whether these should be set or not.

isobmff/CMakeLists.txt

Lines 5 to 7 in 7eaf048

	set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/lib)
	set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/lib)
	set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/bin)