This PR is a work in progress with the goal of getting full support for cphstats into cpptraj. Currently does 4 things:

1. Adds basic cphstats functionality to cpptraj via cphstats analysis command:

  [help cphstats]
	<pH sets> [statsout <statsfile>] [deprot]
	[fracplot [fracplotout <file>]]

statsout: Print cphstats-like output for each input pH data set to .
deprot: Determine things in terms of deprotonated instead of protonated.
fracplot [fracplotout ]: Plot fraction protonated/deprotonated vs pH for each residue.
This does not do any of the more advanced statistical analysis that cphstats does yet.

2. To support 1., add 2 new data sets: one for constant pH data, and one for unsorted constant pH data. Add a datafile class for reading Amber constant pH output.

Read options for Amber CPOUT:
	cpin <file> : CPIN file name.
Write options for Amber CPOUT:
	mcstepsize <nstep> : Monte Carlo step size.
	dt <dt>            : Simulation time step.
	nheader <freq>     : Header write frequency in frames.

3. Add the readensembledata data command:

[help readensembledata]
    <filename> [filenames <additional files>] [<readdata args>]

This is like ensemble but for reading data sets. Works in parallel. Can use fewer threads than ensemble members.

4. Add the sortensembledata command for sorting ensemble data. Currently only works for unsorted constant pH data sets.

[help sortensembledata]
	<dset arg0> [<dset arg1> ...]