More documentation and a few minor updates

[myzie]

Lots of added docs.

Other minor changes and fixes including:

• Remove the time.duration type which was not useful.
• Make time object's string format more helpful.
• Update jmespath to accept other input data types (not just maps).
• Fix panic in CLI when vault is entered without the vault build tag having been used.
• Update math.min and math.max to wrap the corresponding Go standard library functions.

Also moved around a few files in a non-breaking way.

[myzie]

fyi @luisdavim @applejag - see the approach to module docs - markdown files in each module dir, with a make docs-dev Make target to copy them to the risor-site.