Provide history features

[jasonm23]

Draft proposal of history features.

• [x] When a snippet is created, it'll be added to history.
• [x] User can select/expand an auto yasnippet from history.
• [x] User can select/delete an auto yasnippet from history.

README.md updated to provide info about history. Example bindings updated to use an adhoc prefix map, for a nice which-key experience and unify new history features with the existing set of commands.

I'm using parinfer, some additional edits on other sexps are to satisfy it. Package lint is also complaining about several things, but most cannot be satisfied. The other package lint alerts can be satisfied in another PR.

[jasonm23]

• [x] When deleting a snippet the last recorded snippet should become aya-current

it's currently being set to the oldest recorded, after deletion.

[jasonm23]

ref: #24

[jasonm23]

• [x] Manual tests completed locally
  • [x] History is appended to on aya-create
  • [x] History delete of snippet matching aya-current, set current with the most recent recorded snippet.
  • [x] History delete of a snippet not matching aya-current does not modify current.
  • [x] Expand from history prints a message when there is nothing in history.
  • [x] Delete from history prints a message when there is nothing in history.

[jasonm23]

Ready to merge.