Levenberg Marquardt implementation

[vasole]

Addresses #44

[PiRK]

Regarding 4e30789#diff-3ce44ff7792abd000958391cf1b58b70L2, the Sphinx doc says::

in situations where documentation for things in a module is spread over multiple files or sections – one location has the py:module directive, the others only py:currentmodule.

My .. pymodule::directive was wrong, I meant .. py:module::

[payno]

if I understand correctly the line 26 :

"_logger = logging.getLogger(name)"

this is ok if we use this file as a module. But if we use it as a "single file" / demo we will get a warning.

[payno]

Thanks to Thomas it s look like a call to "logging.basicConfig()" before _logger = logging.getLogger(name) is needed when we call it as a "single file"

[dnaudet]

left_derivative is described twice