New schema for parameters

* Improve extra requirement handling
* New mechanism to handle parameters beforehand in chained
  calls, and the ability to get help on available parameters in chained
  calls (through `?help`).
* Redefined Analysis, to reflect the new ontology
* Add parameters as an entity in the schema
* Update examples to include analyses and parameters
* Add processing plugins, with an interface similar to analysis plugins
* Update tests
* Avoid duplication in split plugin

Closes #51

Squashed commit of the following:

commit d145a852e7
commit 6a1069780b
commit ca69bddc17
commit aa35e62a27

docs/bad-examples/results/example-basic-FAIL.json

@@ -6,13 +6,9 @@
   ],
   "entries": [
     {
-      "@type": [
-        "nif:RFC5147String",
-        "nif:Context"
-      ],
       "nif:beginIndex": 0,
       "nif:endIndex": 40,
-      "nif:isString": "My favourite actress is Natalie Portman"
+      "text": "An entry should have a nif:isString key"
     }
   ]
 }