Add documentation and documentation testing

docs/src/submit.md.ejs

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+## submit
+
+`submit(signedTransaction: string): Promise<Object>`
+
+Submits a signed transaction. The transaction is not guaranteed to succeed; it must be verified with [getTransaction](#gettransaction).
+
+### Parameters
+
+<%- renderSchema('input/submit.json') %>
+
+### Return Value
+
+This method returns an object with the following structure:
+
+<%- renderSchema('output/submit.json') %>
+
+### Example
+
+```javascript
+const signedTransaction = '12000322800000002400000017201B0086955368400000000000000C732102F89EAEC7667B30F33D0687BBA86C3FE2A08CCA40A9186C5BDE2DAA6FA97A37D874473045022100BDE09A1F6670403F341C21A77CF35BA47E45CDE974096E1AA5FC39811D8269E702203D60291B9A27F1DCABA9CF5DED307B4F23223E0B6F156991DB601DFB9C41CE1C770A726970706C652E636F6D81145E7B112523F68D2F5E879DB4EAC51C6698A69304';
+return api.submit(signedTransaction)
+  .then(result => {/* ... */});
+```
+
+<%- renderFixture('responses/submit.json') %>