chore(CMakeLists.txt): Use GNUinstalldirs module (#327)
chore(CMakeLists.txt): Use GNUinstalldirs module (#327)

GNUInstallDirs module is available since CMake 3.0.2. It provides
standard install directory variables as defined for GNU software.
Using this module would provides standard variable names for
bindir, libdir, includedir and datadir, etc., which would be
beneficial.

This patch modifies the top-level CMakeLists.txt and apply the
standard variables accordingly. The minimal CMake version requirement
is also bumped to 3.0.2.
rime/librime,rime/librime,rime/librime,rime/librime