[CSLD-162] Add few use-cases to the API doc
[CSLD-162] Add few use-cases to the API doc

Use-cases:
- Sending Money to Multiple Recipients
- Estimating Transaction Fees
- Managing Addresses
- Checking Synchronization Progress
- Managing Accounts
- Retrieving Transactions History

This commits also fixes a few typos (also fixed in 7d576cd8f742f09bf5f5aea8042ecb343497c1c2)
and introduces a paragraph to clarify a bit the monitary units available
in the API.

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype