Add support for threshold dates in filter query expressions

[zerodat]

This PR consists of two commits.

• The first simply removes the generated file src/js/filterlang.mjs from the git repo and adds it to the .gitignore to help keep it from being added to the repo again in future.
• The second commit adds support for threshold dates (with tag t:) to the filter query expressions. This means also adding a jsTodoTxt extension to recognize the threshold date tag during parsing of the todos.

This PR provides a large part of the functionality requested in issue #193, namely the filtering of the todo list based on threshold dates. Still to do in a future PR is the support for updating threshold dates on completion of recurring todos.

[ransome1]

@zerodat I'm out for the weekend and cannot build before Monday. Sorry, I didn't expect you to be so fast ;)

[zerodat]

No problem, @ransome1. Who knows ... maybe I'll have some more for you to merge by Monday. ;)

[zerodat]

@ransome1, adding commits to this pull request to do the following:

• make the filter query expressions a little more forgiving in supporting ISO dates with single-digit month or day, and supporting intervals without a number like today+d rather than requiring today+1d.
• add the code to main.js to support command-line arg for todo file name

[zerodat]

@ransome1, 😄 these are my last commits for this PR, which should merge painlessly with the head of your develop branch.

The last two commits are:

• incorporating @weisserd s fix for the ambiguous sunday problem in sugar. I added this to my PR because his fix is in todotxtExtensions.mjs and that is also a file that I have modified to add the ThresholdExtension. Including it in this PR will make it easier for you to merge I think.
• the bigger commit is to add recurrence support for threshold dates, so that the t: gets updated according to the logic that @amariusz outlined in start date / t: / threshold / defer date / tickler entries support question #193 . Note that I have decided to stick with the past behavior of sleek by adding due dates to todos that have only a rec: tag and neither due: nor t:. But if there is a rec: and a t:, no due: will be added.