Parflow estimator upgrades

[ian-bertolacci]

For #6
Need the following upgrades:

1. Add flag to set ignoring of script exit code (--ignore-script-exit-code)
2. Capture runname in pfrun
3. handle multiple pfruns (the use of multiple pfruns may be limited to test cases, but this is very easy to handle)
4. Better handle other tcl commands in one of two ways:
   a. comment any lines that do not start with a set or pfset command (easy, but ignores possible input effects which may be necessary to calculate parameters).
   b. individually handle pf* commands (tedious, prone to breaking, but potential to handle input effects)

[ian-bertolacci]

1 and 3 handled in 1929e9b