Python API documentation generation tool Code

- Fixed makefile bug

- Register a logger, to print any warnings or errors
- Added a test case for SF bug #1653486 to docbuilder.doctest
- Modified 'specifying constructor signature in class docstring'
examples to eliminate warnings (eg duplicate @type for param)

- Changed print_warnings() to make sure it doesn't register multiple
loggers.

- Added clear_cache()

- Changed MERGE_PRECEDENCE['is_imported'] to introspect -- fixes SF bug
[#1653486].

- Fixed title in epydoc-log.html

- Reduced vertical whitespace space in epydoc-log.html

- Extendedd support for extracting metadata fields from __variables__.
List & tuple values for multival fields are now supported, as are
int, float, bool, and None values (for introspection only -- parsing
still requires string values). Also added several more __varaibles__.

- Added support for extracting metadata fields from __variables__. To
add a new __varaible__->field mapping, set the 'varnames'
variable of the field. Currently supported __variables__ are
__version__, __date__, __author__, __authors__, __license__.
Feel free to add more. Currently, __variables__ are required to have
string values to be considered for addition to metadata.

- Added --include-log option (feature request #1639425). Currently,
it's only useful with --html. The log page is named
"epydoc-log.html", and is linked from the footer.
- Put option defaults in a global dictionary at the top of the
'argument & config file parsing' section
- Added log.close() hook to close logs.