Add the ability to provide a custom document id (aka key) to set using a new command specific option --key. This feature also bumps the major version to 2.0.0.

Requires updating README.md, CHANGELOG.md, and adding new specific tests for this case as well.

Taking on board the feedback in PR #8, I'm feeding back some changes I've found useful.

For consideration:

# DESC: Variable defaults
# ARGS: None.
# OUTS: Variables with default values set.
function defaults() {
  verbose=false no_colour=false cron=false outfile=-
}

...

function parse_params() {
....
  local param
  defaults
  # now enjoy the options in order and nice

Hi,

I'm trying to tackle the (frankly glaring) lack of any repair-enabled UDF fsck under macOS, by (shallow) porting of the still beta (and to-be-merged upstream) fsck, as part of (Linux) udftools (pali/udftools#13).

You can find more details here:

[https://github.com/argorain/udftools/pull/1](https://github.com/argor