String/AbstractString -> ASCIIString
Add a function to check for the existence of a column
implement checkImagingColumnsExist
Merge pull request #14 from mweastwood/improvements

Include checks for whether or not a column exists
Update the README
Add a getting started section to the README
Encourage users to test CasaCore before using
Enable coverage testing
Hopefully fix travis
Oops, fix a name in the coverage script
Use the default testing script
Enable coverage testing
Hopefully fix travis
Oops, fix a name in the coverage script
Use the default testing script
Override default test script