Refactor code

[vedran-kasalica]

Progress:

• Complete removing load_binary from metadata class (make use of functions uniform accross package, i.e. no methods on classes)
• Expose functions at top-level of package
• Somehting else?

Closes #35

[vedran-kasalica]

I finished the following tasks:

• removed load_binary from tsdf class
• fixed read_binary.load_binary_from_metadata

@kretep, you can continue doing the remaining tasks as agreed

[kretep]

This now also addresses #24

[kretep]

The functions are now exposed at the top-level of the package, although the modules are still in there too (not sure how to hide them...)

[kretep]

To be complete: while restructuring the package, I also refactored the tests. The reference to the test data directory was not working properly; now using a plugin for that.

Also simplified and split up the usage documentation (notebooks)

[vedran-kasalica]

The code looks good, the tests and the notebooks were nicely refactored .

[vedran-kasalica]

Closes #24