feat: Add basic, google token and facebook token authentication

[Andrew-Lees11]

Pull request to add client side authentication to KituraKIt

The user adds their authentication to the client using either:

client.addBasicAuth(username: username, password: password) client.addFacebookToken(token) client.addGoogleToken(token)

The correct headers will then be added to all requests to allow authentication with the corresponding TypeSafeMiddlewares on Kitura.

This required internal fields for the request headers and Credentials be added to KituraKit and these are then added to the client request before it is sent.

Docs and tests have been added to cover these changes.

[codecov-io]

Codecov Report

Merging #33 into develop will increase coverage by 4.46%. The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop      #33      +/-   ##
===========================================
+ Coverage    80.15%   84.61%   +4.46%     
===========================================
  Files            2        3       +1     
  Lines          131      169      +38     
===========================================
+ Hits           105      143      +38     
  Misses          26       26

Flag	Coverage Δ
#KituraKit	84.61% <100%> (+4.46%)	:arrow_up:

Impacted Files	Coverage Δ
Sources/KituraKit/ClientCredentials.swift	100% <100%> (ø)
Sources/KituraKit/Client.swift	85.71% <100%> (+2.38%)	:arrow_up:

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[Andrew-Lees11]

LGTM