* Added neutral point (if present)

Closes !gsi-upm/senpy#37 (Ian's)

I've added a neutral point definition (in the converters senpy file) as used in pull request #29

I've used euclidean metric instead of taxicab as I feel it makes more sense (taxicab has bizzare unintuitive effects for points far from the centroids).

Closes gsi-upm/senpy#34

Closes #32

Closes #31

Merge branch 'patch-5' of https://github.com/drevicko/senpy into drevicko-patch-5

'25-validation-errors'
'27-add-method-to-get-list-of-plugins'
'28-fix-multiprocessing-issues'

Closes #28 for python 2.

Apparently, process pools are not contexts in python 2.7.
On the other hand, in py2 you cannot pickle instance methods, so
you have to implement Pool tasks as independent functions.

Closes #28

Added:

* Async test (still missing one that includes the IOLoop)
* Async plugin under tests. To manually try async functionalities:
```
senpy -f tests/
```

Closes #28

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

Closes #26

There was no need to add @list, and it was causing JSON-LD to expand the
URI of 'plugins'

Closes #25

Closes #20

In index.html, there is a suggestion to try out the api with a link to "/api". Clicking that link results in a json error report - not ideal. 
Instead, I added text suggesting that a use can find example api url's after clickgin "Analyse!".

Closes #21

* Alabaster theme
* Restructured
* Simplified introduction
* Reference to entries/models
* Fixed examples

Closes #22

* Improved debugging (back to using Flask's built-in mechanisms)
* Recursive model loading from json
* Added DEVPORT to Makefile
* Accept json-ld input. Closes #16
* Improved Exception handling in client
* Modified default plugin selection to only include analysis plugins
* More tests