fixes several data reader and data source issues
fixes several data reader and data source issues

* fixes #41 data is now passed to load_data, not to the reader
* fixes #39 data caching can be disabled
* fixes #38 data source can accept any args or kwargs
* only data sources with readers that have is_file_reader will look for a filename in args
* update docstrings, :params: should not be sentences, no caps or periods
* in not implemented error just give method name
* change apply_units() to apply_units_to_cache() to make it more clear what it's for
* add example of declaring parameters in the data source class instead of the file
* remove some links, examples and explaination of Python and NumPy regarding comparisons
* create original data source object to use to apply units to cache before checking modification time
* remove constructors for readers that only have parameter as only argument, same as base class
* there is no self.filename in reader anymore, just use filename arg from load_data
* there is no parameters arg in apply_units(), just use self.parameters
* make apply units to numpy data readers private
* apply_units is not a staticmethod anymore, remove from numpy readers, parameterized
 and mixed text xls readers
*

SunPower/Carousel,mikofski/Circus,mikofski/Carousel