docs(operators): Add documentation for fromEvent

[DiedrikDM]

This adds documentation for the fromEvent operator. The documentation has been partially rewritten to clarify certain parts a bit more. This change will close issue #78. Also added an extra innerHTML property binding for the parameter.description to be able to use a hyperlink.

[codecov-io]

Codecov Report

Merging #286 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #286   +/-   ##
=======================================
  Coverage   90.49%   90.49%           
=======================================
  Files         115      115           
  Lines         442      442           
  Branches       10       10           
=======================================
  Hits          400      400           
  Misses         40       40           
  Partials        2        2

Impacted Files	Coverage Δ
src/operator-docs/creation/fromEvent.ts	100% <ø> (ø)	:arrow_up:

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