resolves #74 - Implements primary keys as a specific type

[chaseWillden]

Implements the code recommended from here: #74.

Implements std::str::FromStr for PrimaryKey
Implements std::fmt::Display for PrimaryKey

[vercel]

@chaseWillden is attempting to deploy a commit to the Marcus Cvjeticanin Team on Vercel.

A member of the Team first needs to authorize it.

[chaseWillden]

@mjovanc, as a side, if you recreate your neo.db table, I'd probably change:

id TEXT PRIMARY KEY,
neo_reference_id TEXT

to

id INTEGER PRIMARY KEY,
neo_reference_id INTEGER

[mjovanc]

@chaseWillden Thanks for the PR. LGTM. However the code inside njord_examples will be changed at a later point. Need to fix the id field in the proc macro first.

But thanks a lot for the help!