New annually-varying serotype distribution; other changes too

Users can still specify a single serotype distribution on the command line.
Alternatively, they can specify a serotype file with four floats per line, each
line corresponding to one year.  If a simulation is run for more years than
lines in the file, the values are repeated from the beginning.

Utility header has been split into a header and cpp file.  Further refactoring
is probably approrpriate.

The string split function has been replaced with one that is much more readable.

The max run length is now 15000 days.  This parameter probably is not needed.
Moving paho_cases file to the pop-yucatan directory
New ABC attempt - 34 year simulation, changed parameters and metrics
Merge branch 'master' of https://github.com/tjhladish/dengue