[FTG] Compare module (#185)

* Introduced new Fortran module `m_ser_ftg_cmp.f90` which contains one public subroutine (interface)  `ftg_compare` for the FTG interface that compares size and content of a passed variable with a stored one from the Serializer.
I'm not very happy with the module name, too many underscores, so if someone has a better idea...

* Also added unit test `ser_ftg_cmp_test.pf`.

* Cleaned up `m_ser_ftg.f90`:
  * Removed unused function `ftg_match_size`.
  * Removed unused `bounds` variables in scalar versions of `ftg_allocate_*`
  * Removed blank lines

* Various changes in `ser_ftg_test.pf`.

* Fixed C library name in Python module `serialbox/common.py` => `SerialboxCShared`.

************************
`m_ser_ftg.f90` and `m_ser_ftg_cmp.f90` were generated with [**FortranGenerictor**](https://github.com/chovyy/fortrangenerictor) from [`m_ser_ftg.f90.cht`](https://github.com/chovyy/fortrangenerictor/blob/ftg-compare/m_ser_ftg.f90.cht) and [`m_ser_ftg_cmp.f90.cht`](https://github.com/chovyy/fortrangenerictor/blob/ftg-compare/m_ser_ftg_cmp.f90.cht).
************************

Author: Christian Hovy

Diff for: src/serialbox-fortran/CMakeLists.txt

@@ -21,7 +21,7 @@ if(SERIALBOX_ENABLE_FORTRAN)
 
   set(SOURCES_FORTRAN utils_ppser.f90 )
   if (SERIALBOX_ENABLE_FTG)
-    set(SOURCES_FORTRAN ${SOURCES_FORTRAN} m_ser_ftg.f90)
+    set(SOURCES_FORTRAN ${SOURCES_FORTRAN} m_ser_ftg.f90 m_ser_ftg_cmp.f90)
   endif()
 
   add_library(SerialboxFortranObjects OBJECT ${SOURCES_FORTRAN})