Bugfixes

Note: If you're using sparse matrices to create loom files, this update fixes a nasty performance bug (see #48)

Bugfixes

• Exception when assigning a layer directly on the connection object:

with loompy.connect("filename.loom") as ds:
    ds["layername"] = m

• Severe performance bug when creating from large sparse matrix (issue #48)
• Error in example of valid file format (issue #44)
• Improved handling of connections opened in readonly mode (see commit d92bac9)