feature(tags): measure how long time spent on a single tag takes in a simple way
feat(tags): add extra time-based functions

* `tags#getSpan() => Int` - works out the ~total amount of time,
    in minutes, that has been tagged so far.

* `tags#getTimeTotalFor(tagname:String) => Int` -  works out the
    ~total amount of time spent doing a named part or whole tag.

* `tags#getTimesAfterMidnight() => Array<Times>` - finds the
    ~total times for each tag after midnight.
refactor(api): rework some of the api routes.

add: GET /api/time/ - get the total time tagged so far
add: GET /api/time/{name} - get the total time tagged for {name}
add: GET /api/today/time - get an array of tags with durations for today

remove: GET /api/count/tag/{name}
remove: GET /api/time/tag/{name}

also updated how GET /api/today/time/{name} works:
now works out the ~total duration spent on {name} today

BREAKING CHANGES: removed two API endpoints,
* GET /api/count/tag/{name}
* GET /api/time/tag/{name}
chore(ebnf): add grammar for my tags as example
docs(ebnf): move grammar file into docs folder
Merge branch 'feat/howlong' into development