Add Donation API documentation page.
Add some more field descriptions.
Fix json syntax errors.
Fix a couple of json syntax errors.
Complete a few field descriptions.
Fix typo.
Fill in the remaining missing descriptions.
Wordsmithing.
Improve the description of the 'amount' field.
Complete the sentences in the endpoint descriptions.

Remove extraneous word from the 'amount' field description.
Add link to election period code table.
Merge pull request #1 from 3dna/miki/update_donations_api_doc

Miki/update donations api doc