TODO in vex2difx

x. Capitalization of Antenna names and obs code
x. # sign
x. load params file
x. Pulsar support
x. Spacecraft support
x. Handle files (i.e., not Mark5 modules)
7. Handle multiple phase centers
x. full paths to files
x. guardblocks, blocks per send
10. what to do about modes that don't support all antennas? (c081a.skd currently fails)
	- Adam suggests populating a bogus datastream entry with no corresponding baselines
x. support mark5b
12. support VDIF
x. support baselines=
x. implement maxLength
x. use antennas, not modules, in antenna count
x. support time formats other than mjd
x. support EVLBI
18. clean up oversampling/decimation support
19. Clean up antenna names/defs as done for sources
20. Currently corrparams is used both during vex parsing and at input building time.  It would be nice to eventually make the vex parsing independent of corrparams.

Concerns outside vex2difx proper

x. Need ant velocities and pos'n epoch in vex file
	- what is a year?  not everyone thinks it is 365.25 days
x. Need to get module shelf location from track 
3. Calcode/Qualifier in vex
x. Get exper_nominal_{start,stop} in vex files