* Add Topic model
* Add PDB post-mortem debugging
* Add logger to plugins (`self.log`)
* Add NLTK resource auto-download
* Force installation of requirements even if adding doesn't work
* Add a method to find files in several possible locations. Now the plugin.open
method will try these locations IF the file is to be opened in read mode.
Otherwise only the SENPY_DATA folder will be used (to avoid writing to the
package folder).
It turns out setting "plugins" as a @list in the context causes the
"plugins" property to expand to its full name.
Removing the type causes a regression of #17, which I initially missed
because the test in #17 was wrong.
Closes#26