Ignore build files
Example update - ParaView 4.2

Due to a few changes in the filters with ParaView 4.2, the examples had
to be adjusted. These versions will therefore not work in ParaView <
4.2  versions.
In addition, added proper import commands as pv_atmos is now on pypi,
and the files first check if the input files actually exist before
running the code.
Re-arrangement for packaging

For more convenient packaging, atmos_basic and atmos_grids have been
rendered completely independent.
This means that Lin2Log() and BoundAspectRatio() have been moved from
atmos_basic to atmos_grids. This was a natural re-arrangement which
makes more sense.
Also, MakeSelectable() resides in atmos_basic, and can therefore not be
called in atmos_grids. This has been corrected as well.
Merge branch 'master' of https://github.com/mjucker/pv_atmos

Conflicts:
	atmos_basic.py