Use meson build system

[swesterfeld]

Currently we use automake / autotools as build system. This is problematic due to two reasons:

• automake is slow (because it runs lots shell scripts and doesn't track dependencies nicely for subdirs)
• automake is not a good solution for Windows users, because Windows does not ship with a shell

Using meson (which is the more modern approach) should fix both issues. Also the actual build rules will look cleaner after porting configure.ac / Makefile.am files to meson.build files.