Build system bug fixes and cleanup

The following issues have been addressed in the 1.3.4 release:

1. 🔨 Reduce the complexity and duplication of the CMake build system (issue #58)
2. ♻️ Add uninstall target to CMake generated makefile; after installing OpenCoarrays, type make uninstall from the build directory to remove OpenCoarrays. Other software dependencies will not be touched.
3. 🪲 Fix flip-flopped user yes/no (y/n) selection confirmation in install.sh installation script.
4. 🎱 Default to yes (Y) for installation script options to perform a default build (issue #35) so that yes | install.sh or hitting <return> repeatedly will produce a non-interactive default installation.
5. ⬇️ Download prerequisite packages using .bz2 or .gz compression, not .xz compression which might be missing on some older systems.
6. ☁️ Fix problems fetching install prerequisites on linux with FTP (issue #123)

Commits and detailed changes from 1.3.2:point_right:1.3.4

OpenCoarrays-1.3.4.tar.gz is the release archive. The other files are the cryptographic hash and GPG signature of the hash to verify the authenticity of the release archive.