MAINT: NEXRAD archive file now returned with float32 fields
MAINT: added replace_existing parameter to add_field method.
Merge pull request #181 from jjhelmus/master

MAINT: float32 NEXRAD fields and replace_existing parameter
BUG: Fixed cfradial unit test to work with netCDF4 >= 1.1.1

See https://github.com/Unidata/netcdf4-python/pull/269 for change in
netCDF4 library.
Merge pull request #183 from jjhelmus/bug_netcdf_maskandscale

BUG: Fixed cfradial unit test to work with netCDF4 >= 1.1.1
Adding arm_time_variables parameter to write_grid

I am adding the 'arm_time_variables' parameter to the write_grid
function in the grid_io module. This is consistent with the parameter of
the same name found in the cfradial module.
Adding arm_time_variables to write method

Similar to the previous commit, but this time adding the
arm_time_variables to the Grid object write method.
Checking PEP 8 standards...

All changed files now meet PEP 8 standards!
Merge pull request #184 from kirknorth/grid-arm-vars

Add arm_time_variables to Grid I/O