Ideas for changes in the internal structure

[hamogu]

Just some small ideas to simplify things in asciitable. This post does not mean that I offer to implement that soon, I just want to make sure these things do not get lost.

• formatter and converter really do the same thing, one for input, one for output. That could be unified.
• MemoryReader should recognize numpy masked arrays and use the mask in some way on output. After all, masked arrays are the default output, if a table is read with fill_values.
• Outputter as a class are only used when reading a table, maybe we should use the same structure for writing.

[taldcroft]

Active development will continue with astropy.io.ascii. Transferring (in slightly modified form) to an issue there.