Modified: mywrangle.py and simulate_cmd.py

- Created large structured arrays containing a wide
  range of Dartmouth isochrones with various [Fe/H],
  [alpha/Fe], and age (see file make_library.py in
  dartmouth/isochrone dir).

- One file is available for each of five photometric
  systems, SDSS (AB), CFHT_SDSS (AB), WFPC2, WFC3, ACS (STMAG)

- Conversions between VegaMAG -> STMAG are done in make_library.py

- Data is saved as structured numpy arrays and pickle objects, and
  contain only the relevant magnitude bands for the project. Additional
  bands as well as finer grids in age, feh, and afe can be read-in and
  the isochrone library remade by suitably modifying usecols = (...) and
  dtypes_read = [( ),( ),( )...] in make_library.py

- mywrangle.py:
  - created read_iso_darth module to read-in the data from the libraries
    selected above.
  - the older file reading in text files is temporarily assigned name
    read_iso_darth_txt, but will be deprecated from now on.
  -WARNING: read_phot still has not been updated to take in the variables
    system, sysmag1, and sysmag2, or perhaps this can be specified outside
    of the module and within the main program instead. sysmag1, sysmag2 are
    the bands being fit. each data set only has two bands so maybe it won't
    be necessary to specify bands in read_phot.

- simulate_cmd.py:

  - This code consists of a module simulate_cmd, as well as some test code
    to call that module and output a simulated cmd.

  - simulate_cmd now takes in (required) string variables sysmag1, and sysmag2,
    immediately after variable system.

  - The following can be specified to create dummy datasets, currently just
    written within file.
    system = 'acs'
    sysmag1   = 'F606W' #color = sysmag1 - sysmag2
    sysmag2   = 'F814W' #sysmag2 = the magnitude
    age = 14.0  #age of system desired
    feh = -2.5  #feh of system desired
    afe = 0.4   #idem for [alpha/Fe]
    dmod = 20.63  #dmod to Hercules
    nstars = 10000  #number of stars in MC
    mass_min = can be specified, currently in argument call to simulate_cmd
    mass_max = can be spcified, currently in argument call to simulate_cmd

  #WARNING: Currently passing a single mag, magerr array to simulate_cmd,
   but presumably each band will have its own magnitude error profiles as
   a function of magnitude.