Add the option formatted to script odfdo-replace and method Element.replace() to interpret the space, tab and CR of the replacement string.

Fix a bug on Document.insert_style() and related methods that prevented
the loading of styles from the family number:*, like number:currency-style (issue #53).

• Refactor cell properties to get easier and more consistent access to cell values. Some new properties added: Cell.decimal, Cell.int, Cell.bool, Cell.duration, Cell.datetime, Cell.date.
• Add a .rdf manifest file if it is missing (this should only happen in very rare manipulations).

• Refactor Table and Row caching, removing useless _caching attribute from many classes.
• Remove module scriptutils.

Allow XML export of base64 encoded images (preparing for flat ODF export).

• The Meta class which manages the meta.xml part has two new methods as_dict() and as_json() to export its content.
• Improved "pretty" export of documents.

Fix some small rendering issues for Markdown export.

• Change in str(Paragraph) which now includes a '\n' at the end of the string.
• The odfdo-to-md script is renamed to odfdo-markdown and should be functional. Markdown export of .odt files supports all standard formatting features (including tables) except quoted text (no clear semantic equivalent in the ODF standard).

• New script odfdo-to-md to export text document in markdown format to stdout (experimental, do not export images links neither tables).
• Fix VarTime initialization: class can now be initialized without mandatory time argument.

Improvement of documentation. The HTML documentation in /doc (mostly auto generated) contains now all recipes, sorted by relevance.