Nngt

Various corrections and improvements.

**Improvements**
* plot_activity has axis keyword and better color handling
* get_weights/delays/types support partial edges query
* draw_network with colorbar

**Bugfix**
* edge_list and neighbour_list attributes saving
* problems with network saving in db
* get_weights
* get_node_attributes
* nx edges_attributes and BaseGraph new_edge_attr
* inverted in/out neighbours for igraph

I think NNGT is now fully release ready, so this is officially 1.0.0.
You can now install it from pipy using pip on any platform.

Changelog:

* Updated documentation
* Improved config
* New load_from_file function
* Added check for duplicated edges (in the newly added edges only) + empty edges addition in new_edges
* Wrapped NEST functions to improve interactions (groups and network.nest_gids are now reset by nest.ResetKernel)
* Support for non-scalar arguments in neuron_params when creating nest network
* set_minis now take synaptic type into account (different call for mEPSCs/mIPSCs)
* Improved graph libraries handling for new edges
* Corrected "neighbout list" IO (errored)
* Corrected database to work with peewee>=3
* Corrected network plotting
* Icreased testing
* logging is always on a single MPI process
* corrected mpi checker

New default backend, which does not require any additional graph library.
Allows for fully distributed graph generation and storage to use with NEST on clusters.

Full I/O is now available with shape and population included in the file.
MPI-parallel I/O was also added.

Gaussian-degree is now available for MPI generation, in addition to distance-rule, which now includes a Gaussian kernel.

Corrected a wrong test that made groups only able to be either sources or targets but not both at the same time.

A lot of internal improvements have been added and the basic functions have been more thoroughly tested.

* Improved plotting tools and analyses (added automatic binning + basic network drawing)
* Better attributes handling
* Additional correction to networkx, igraph and graph-tool handling
* Shape is now saved in IO
* Using logging

With this new release, three main updates have been added:

* support for custom network spatial structures through the ``geometry`` module, from the SENeC package [``PyNCulture``](https://github.com/SENeC-Initiative/PyNCulture). So far, edge distance is still computed as the simple distance between neurons, not taking potential obstacles into account.
* multithreaded algorithms for ``fixed/gaussian_degree`` methods, as well as the ``distance_rule`` generator.
* ``set_minis`` method to simulate synaptic noise from spontaneous release of neurotransmitters.

Other improvements:

* added logging
* removed ``globals.py`` and moved features to ``lib``
* improved support for edge attributes (still a work in progress)
* custom graph plotting with matplotlib (work inprogress)

Planned improvements for next release:

* support of all main graph formats for IO
* full support of node and edge attributes
* more complete tests for Travis