Modify installation instructions for gost-engine library and module

- Simplify the installation of libraries and programs to simply use
  defaults.
- Install only the gost engine in module form into the OpenSSL engine
  directory.
- Install the gostsum and gost12sum manuals in the normal man1 directory,
  as there's really no reason to install them among OpenSSL stuff
  specifically.
- Install the cmake configuration file.