Support for antenna pointing corrections

[vsmagalhaes]

Support for antenna pointing corrections is to be implemented in astrohack.
This will most probably include two functions:

• extract_peek: Function that extracts visibilities from a pointing observation MS.
• peek: Function that process extracted data to produce antenna pointing corrections.

AIPS' code for the task PEEK will probably serve as a base for this, specially regarding pointing models to use, desired output formats and interesting plots to facilitate analysis.