CMake installation issues

[nilsnolde]

I just wanted to update our docker setup which hasn't been able to build new images in a month and I found prime_server has some problems on several installation routes with our ubuntu 20.04 base image:
With the CMake install from the README, Valhalla wouldn't be able to find libprime_server:

-- Checking for module 'libprime_server>=0.6.3'
--   Requested 'libprime_server >= 0.6.3' but version of libprime_server is
CMake Error at /usr/share/cmake-3.16/Modules/FindPkgConfig.cmake:463 (message):
  A required package was not found
Call Stack (most recent call first):
  /usr/share/cmake-3.16/Modules/FindPkgConfig.cmake:643 (_pkg_check_modules_internal)
  CMakeLists.txt:208 (pkg_check_modules)

The usual autotools install works (i.e. valhalla's CMake recognizes it), but I also get timeouts on the tests as in #99 (EDIT: on another clean try, that wasn't the case anymore.. weird..). Curiously enough, the tests do work with CMake build!

Well, I found out what the issue is while writing this 😅 PR on the way (VERSION was not set in CMakeLists, so the pkgconfig template didn't set the version).