convert: enum lookup has a mandatory raw datfile type
convert: added enum for possible garrison units
convert: better exception when enumlookup fails
convert: enums for unit class and terrain restriction introduced
convert: enums for various fields created

also added a lot of descriptive comments
convert: fixed wrong reading offset when reading projectile unit data

we read a int16_t instead of a float, and I added 2 padding bytes
later to compensate the resulting float errors.
convert: inheritance display uses repr(class) instead of repr(object)
convert: more comments and enums for the dat file
Merge branch 'convertdat'