Fix templated constructors regression

Templated constructors were incorrectly ignored because SWIG thought they were
methods without a return type.
Regression introduced in swig-3.0.0
Closes #245.
Merge latest master into doxygen branch.
Don't indent Doxygen doc strings in generated Python code.

This is unnecessary and inconsistent with "builtin" case in which the
docstrings are not indented in the generated C++ code, thus making it
impossible to write tests working in both cases.

Most of the changes in this commit simply remove the extra whitespace from the
expected values in the tests.
Use class docstrings in "-builtin" Python case.

Put the docstring into tp_doc slot which exists exactly for this purpose.
Fix Doxygen unit test in Python "-builtin" case.

Unfortunately there doesn't seem to be any way to use docstrings for __init__
methods when using "-builtin", so just disable this particular test then.