Ptable

* Added `add_column` method to enable building tables up column-by-column.
* Added `print_HTML` and `get_HTML_string` methods to enable HTML table
production.
* Added `set_border_chars` method to enable control over characters used to
draw the table border.
* Added `set_left_padding` and `set_right_padding` methods to allow
independent padding control for both sides of a column.
* Added `sortby` option to enable column sorting.
* Added `header` option to enable switching off field name printing at top of
table.
* Modified `hrules` option to enable greater control over presence of
horizontal lines.
* Added `border` option to enable switching off all line printing.

Thanks to Tim Cera, Chris Clark, Alexander Lamaison for suggesting and helping
to test many of the new features in this release.

* Added `padding_width` option to control the number of spaces between the
vertical line rules at the edges of a column and its content. This can be
set as a keyword argument to the constructor or after instantiation using
the `set_padding_width` method. The value is set to 1 by defaut. If your
table is too wide for a small screen with this value, setting it to 0 might
help you squeeze it in.

Thanks to Chris Clark for contributing a patch against 0.2.1 to add this
feature!

* Caching no longer breaks when using the `printt(fields=[...])` syntax. The
list of fields was not hashable and hence could not be used as a dictionary
key. I fixed this using the output of the `cPickle` module's `dumps`
function as the dictionary key instead.
* Horizontal lines are now the appropriate length when the above syntax is
used.

Thanks to Julien Koesten for reporting these bugs and testing the fixes almost

* Added `get_string` method.
* Added `__str__` method (which just calls `get_string`) to enable nice
`print x` syntax.
* Can now pass field names as a constructor argument.
* Return values of `get_string` are cached in a dictionary that is only
cleared after a call to `add_row` or something else which invalidates the
cache.

* Original release.