MCPL release 1.6.0

Another release with multiple CMake-configuration improvements. Most visibly, most high-level CMake options were renamed so their names are now prefixed with MCPL_ and use a more consistent naming scheme (#67). For example BUILD_EXAMPLES is now instead MCPL_ENABLE_EXAMPLES, find more variables by looking here. For now, it has been attempted to remain backwards compatible and support the old variables as well, but it is highly recommended to migrate to the new variables as soon as possible.

The dependency on ZLIB has been made more flexible. The new option MCPL_ENABLE_ZLIB is more flexible and supports one of several values: IFAVAILABLE, FETCH, USEPREINSTALLED, ALWAYS, OFF, or NEVER. The default value of IFAVAILABLE will try to locate ZLIB, but will simply disable ZLIB support if unsuccesful. The identical options OFF and NEVER are obviously simply disabling ZLIB support irrespective of presence on the system. The option ALWAYS will attempt to find ZLIB on the system, and if it fails it will instead fetch the zlib sources from the official zlib location at github, and build the appropriate capabilities right into the MCPL binaries. The option, USEPREINSTALLED is actually like the old default behaviour: look for ZLIB on the system and fail if it it is not available. Finally, the option FETCH will always fetch sources online, ignoring any ZLIB already present on the system.

A few other hidden expert-only options (MCPL_ENABLE_CPACK, MCPL_DISABLE_CXX) were added as well, supporting various integration and packaging efforts.