Asciitable

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Add IPAC reader and reader comment_lines attribute plus doc updates.

- Add IPAC format reader

- Add 'comment_lines' attribute to BaseReader class to return all lines
matching the header comment character.

- Made the table lines retrieved by the Inputter available as the
Reader object 'lines' attribute in the BaseReader.read() function.

- Updates and reorganization of doc-strings and documentation

- Removed the non-working code related to mask support (try again later)

- Added 'meta' and 'keywords' attributes to BaseReader and added a Keywords
class. This is a placeholder for future support of table metadata.

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Add support for reading CDS format files (header + data in one file)

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Updates to the way lines are processed and comments handled for support of new formats.

- Splitter process_line and process_val and Inputter process_line are now object methods.
This allows for settable parameters that control processing (e.g. continuation_char).

- Add BaseHeader and BaseData process_line methods that do comment and blank-line
filtering as needed. Splitter process_line should no longer be used for this purpose.

- Add support for formats:
- CommentedHeader (column def line begins with comment char)
- DAOphot
- Files with continuation lines via ContinuationLinesInputter class

- Add 'Inputter' as an option to get_reader() and read()