Add basic V2 documentation to the README

Oxford Dictionaries has discontinued their V1 API (it will be taken
offline on June 30, 2019). As part of the upgrade of this wrapper the
new interface uses named parameters.

Reference the following PRs for the new usage:
- Entries: #8
- Translations: #12
- Sentences: #13
- Thesaurus: #14
- Lemmas: #10
- Search: #15

All of the response objects are OpenStructs with camelCase keys. This is
a departure from V1 (which used snake_case keys in the response).

README.md

@@ -19,69 +19,67 @@ client = OxfordDictionary::Client.new(app_id: 'ID', app_key: 'SECRET')
 client = OxfordDictionary.new(app_id: 'ID', app_key: 'SECRET')
 ```
 ### Usage Examples
-Some documentation on the different endpoint function calls can be found [here](http://rubydoc.info/gems/oxford_dictionary/OxfordDictionary/Endpoints)
-
 This wrapper follows the schema laid out by the API quite closely. The data
 schema for the different API calls can be found [here](https://developer.oxforddictionaries.com/documentation).
 
-###### Get the results for an entry
+###### Entries
 ```ruby
-entry = client.entry('vapid')
+entry = client.entry(word: 'vapid', dataset: 'en-gb', params: {})
 
 # Access the first entry
 # Refer to the API documentation for the schema of the returned data structure
-first_lexical_entry = entry.lexical_entries[0]
+first_lexical_entry = entry.lexicalEntries.first
 
 # With some filters
 filters = { lexicalCategory: 'Verb', domains: 'Art'}
-client.entry('truth', filters)
+client.entry(word: 'truth', dataset: 'en-gb', params: filters)
+
+# You can also search for the results for different datasets
+# Refer to the Oxford Dictionaries documentation for all the
+# possible datasets
+client.entry(word: 'ace', dataset: 'es', params: {})
 
-# Or do them "inline"
-client.entry('truth', lexicalCategory: 'Verb', domains: 'Art')
+# You can query for results from a specific "field"
+# Refer to the Oxford Dictionaries documentation for all the
+# possible fields
+client.entry(word: 'explain', dataset: 'en-gb', params: { fields: 'examples' })
 
-# From a dictionary of a specific language (default is 'en')
-client.entry('ace', lang: 'es')
 ```
 
-###### Or return some subset of information
+###### Lemmas
 ```ruby
-# Like just the examples
-examples = client.entry_examples('explain')
-
-# Or only the pronunciations...
-the_noises = client.entry_pronunciations('knight')
-
-# Or the translations (for Swahili in this example)
-en_to_es = client.entry_translations('change', translations: 'sw')
-# If no :translations filter is supplied, default is 'es'
-
-# Or some of the other documented API calls
-client.entry_sentences('scholar')
-client.entry_definitions('correct')
-client.entry_antonyms_synonyms('monotonous')
-# Etc...
-
-# Generally the method names follow the documented API closely
+client.lemma(word: 'condition', language: 'en', params: {})
 ```
 
-###### Other endpoint calls
+###### Translations
 ```ruby
-# Or the search endpoint
-search_results = client.search('condition', prefix: true)
+client.translation(
+  word: 'condition',
+  source_language: 'en',
+  target_language: 'es',
+  params: {}
+)
 ```
 
-###### A quick note on how to add filters to queries
-There isn't much argument checking at the moment.  Some endpoints do not accept filter arguments, refer to the API documentation to check for endpoints that accept filters.
+###### Sentences
 ```ruby
-# All endpoints accept the :lang filter.  This specifies which dictionary to use
-# If no argument is supplied, default is 'en'
-filters = { lang: 'es' }
+client.sentence(word: 'paraphrase', language: 'en', params: {})
+```
 
-# To use multiple values on a single filter, make it an array
-filters = { lexicalCategory: ['Noun', 'Verb'] }
+###### Search
+```ruby
+client.search(language: 'en-gb', params: { q: 'vapid' })
 ```
 
-Argument names need to be in camelCase, not snake_case. However, the objects returned from API calls use snake_case attributes.
+###### Thesaurus
+```ruby
+client.thesaurus(
+  word: 'book',
+  language: 'en',
+  params: { fields: 'synonyms,antonyms}
+)
+# Or use { fields: 'synonyms' } for just synonyms
+```
 
 ## Development