Endpoint /words:

Use this endpoint to retrieve definitions, examples and other information for a given dictionary word or an inflection (e.g., running > run). The response contains information about the lemmas to which the given word/inflected form is linked.

Sometimes it generate entries with only "homographNumber" and "inflections"; such entries are a sole lexical category if displayed.

Should I revert to /entries endpoint? If so, I need to query /lemmas first to get the headword, and then use /entries.

1. One RetrieveEntry has at least one HeadwordEntry
2. One HeadwordEntry has at least one LexicalEntry
3. Each LexicalEntry has one and only one
   1. LexicalCategory (single object)
   2. Entry (array of length 1)
4. Each Entry
5. Each Sense if has definitions then only one (array of length 1)

Before

Even oxd --help will fail if the environmental variables are missing. Moreover, the error message doesn't tell what is missing or how to fix that.

$ oxd --help
Problem reading Oxford Dictionary API App KEY: environment variable not found

After

• oxd --help works all the time.

• $ oxd rust  # without env variables
  Problem reading Oxford Dictionary API App KEY: environment variable not found
  Get one at https://developer.oxforddictionaries.com/ and set OD_API_APP_KEY.
  

• [x] #5
• [x] #7
• [x] Play audio (only once for the same pronunciation) when using terminal
• [x] #2
• [x] Error handling
  • [x] API call return error code
  • [x] Not very clear how to sanitize user input
• [x] Use words endpoint instead ~Convert lemma to headword~
• [x] Replace and remove API id and key
• [x] Add variantForms (such as those in word fetid: British foetid)