cmake: remove dead code

Simply linking to "marsyas" target works even if it is a static library,
confirmed on Linux and OS X.
user manual: relax wording about CMake as requirement
user manual: update info on required compilation tools
user manual: suggest usage of latest development version

The process of building the last stable release differs significantly from
the current development state so the user manual does not apply to the
last release anymore.

Since we are approaching the next stable release, I suggest any new user
to use the current development version.
user manual: add detailed instructions to build latest sources on Windows
user manual: cleanup - no need for explicit node navigation links
user manual: fix (sub)sectioning