Add an implicit conversion to double for unitval type.

Allow us to assign a unitval to a double, stripping off the units in
the process.  This isn't technically necessary for adding the
additional RF reporting; however, it's a small enough change that I
thought I'd piggyback it here.

Also, remove an unnecessary line in unitval::unitval(double,
unit_types).  Also a small change.
Add GETDATA capability for all forcing contributions.

The forcings added were CO2, CH4, N2O, H2O, O3, BC, OC, SO2 (direct,
indirect, and combined), and volcanic.  Total forcing and the
halocarbons were already in.
Changes to ensure consistency in the O3 component:

* D_ATMOSPHERIC_{NOX,CO,NMVOC} -> D_EMISSIONS_{NOX,CO,NMVOC}, since
  these are emissions, not concentrations.
* Change the unit on NOX from Tg-NOX to Tg-NO, since that is what is
  in our input data files.
* Changes as necessary in the ini and emissions files, since some of
  the labels for these gasses have changed.
Update README.md
Merge pull request #32 from JGCRI/o3-fix

Changes to ensure consistency in the O3 component:
Merge pull request #31 from JGCRI/rf-reporting

Rf reporting
Merge pull request #35 from JGCRI/master

updating CH hector to master 10/07/14