Rename later to fromNow to clarify the origin time

[jporsay]

Using .later doesn't leave clear what the origin time is.
Renamed it to .fromNow to clarify that the time is a delta time starting from DateTime.now().

3rd party examples:
moment.js uses a similar nomenclature.
As does Ruby on Rails.

Fixes #9

[codecov-io]

Codecov Report

Merging #8 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #8   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          13     13           
=====================================
  Hits           13     13

Impacted Files	Coverage Δ
lib/src/extensions.dart	100% <100%> (ø)	⬆️

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[jogboms]

Hey @jporsay
This is indeed a good catch.
Thanks, but can I ask that we keep this open for a while and pinned? As it is a grammatical and/or semantic change that may not affect as much unless needed.

[jporsay]

No problem with me. Also, not quite sure why you tagged it as help-wanted when the changes have already been done ;)

[jogboms]

Yeah, I want more eyes to see this but apparently PR's don't work that way.