Issue 137... : simultaneous building of both shared and static libraries.

Re-enabled support for building both static and shared libraries by default.

To avoid clobbering the import lib emitted by msvc, I did as CMake has documented:
http://www.cmake.org/Wiki/CMake_FAQ#How_do_I_make_my_shared_and_static_libraries_have_the_same_root_name.2C_but_different_suffixes.3F

If you'd like both the static lib and the import lib to be named "capstone.lib", then we can probably explicitly specify the OUTPUT_DIRECTORY for each target, or change the {ARCHIVE,RUNTIME}_OUTPUT_NAME for the capstone-shared target.