New files added.  These take functions previously in diploid_functions.tcc and separate them out based on what type of simulation they are used for.
Removed unnecessary #includes and added #includes to new .tcc files
added new .tcc files to pkginclude_HEADERS
Metapop version of sample_diploid: moved where tpop is updated.  Moved where (dptr+i)->first is updated so that the code block updating the offsrping looks like the single deme version. Moved comments around so that they appear first where needed.