sofa v0.3.0

NEW FEATURES

• Gains new functions db_index, db_index_create, and db_index_delete
  for getting an index, creating one, and deleting one
• Gains function design_search_many to do many queries at once
  in a POST request (#56)
• design_search reworked to allow user to do a GET request or
  POST request depending on if they use params parameter or
  body parameter - many parameters removed in the function
  definition, and are now to be passed to params or body (#56)
• db_alldocs gains new parameter disk to optionally
  write data to disk instead of into the R session - should help
  when data is very large (if disk is used fxn returns a file path) (#64)

MINOR IMPROVEMENTS

• fix minor issues in vignette, and updated for working with CouchDB v2 and greater (#53) (#54) (#47)
• replace httr with crul for HTTP requests (#52)
• design_copy removed temporarily (#20) (#60)
• new issue and pull request template

BUG FIXES

• Fix to docs for design_search (#57) thanks @michellymenezes
• Fix to db_query to make a single field passed to fields parameter
  work (#63) thanks @gtumuluri
• Fix error in doc_attach_get (#58) thanks @gtumuluri