Add Altitude variables to LevelC2 ACCP files

[patricia-nasa]

Users are requesting that altitude information be included in A-CCP LevelC2 files (merged lidar files).
New version of ext_sampler.py writes this out, and latest 2053 nm ext files (lidar LevelC files) do include altitude variables.
Need to modify merge_lidar.py to merge 3 new variables ze, pe, and te (layer edge altitude, pressure, and temperature) to the LevelC2 files.