fix: make StaticFileServer open class

[Andrew-Lees11]

Description

In this pull request the StaticFileServer and its handle function were changed from being public to being open.

Motivation and Context

This was done to fix issue #937 and allow you to subclass/override the class.

How Has This Been Tested?

Kitura tests have been run and all pass.

[ianpartridge]

Please remove the Jazzy docs changes, we have a separate process for generating those now via the jazzy-docs GitHub label.

[codecov-io]

Codecov Report

Merging #1245 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1245   +/-   ##
=======================================
  Coverage   89.07%   89.07%           
=======================================
  Files          38       38           
  Lines        2280     2280           
=======================================
  Hits         2031     2031           
  Misses        249      249

Flag	Coverage Δ
#Kitura	89.07% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
...ces/Kitura/staticFileServer/StaticFileServer.swift	94.73% <100%> (ø)	⬆️

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[ianpartridge]

Now this removes the Jazzy docs altogether 🤣

Sorry, I meant leave them unchanged...