[Enhancement] DocC documentation support (#23)

This PR contains the work done to add DocC support to all the libraries included in this package, as requested by issue #9.

To provide further details about the work done:
- [x] added the DocC plugin package as a dependency
- [x] improved the naming of the targets in the Package file
- [x] updated the README file
- [x] implemented the Xcode and Github pages documentation generation targets in the Makefile file
- [x] generated both Xcode and Github pages documentation

Reviewed-on: #23
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

docs/swift-libs-communication/css/documentation-topic~topic.fccbd76c.css

@@ -0,0 +1,9 @@
+/*!
+ * This source file is part of the Swift.org open source project
+ * 
+ * Copyright (c) 2021 Apple Inc. and the Swift project authors
+ * Licensed under Apache License v2.0 with Runtime Library Exception
+ * 
+ * See https://swift.org/LICENSE.txt for license information
+ * See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */.generic-modal[data-v-f5b28690]{position:fixed;top:0;left:0;right:0;bottom:0;margin:0;z-index:11000;display:flex;align-items:center;justify-content:center;flex-wrap:wrap;background:none;overflow:auto}.modal-fullscreen[data-v-f5b28690]{align-items:stretch}.modal-fullscreen .container[data-v-f5b28690]{margin:0;flex:1;width:100%;height:100%;padding-top:env(safe-area-inset-top);padding-right:env(safe-area-inset-right);padding-bottom:env(safe-area-inset-bottom);padding-left:env(safe-area-inset-left)}.modal-standard[data-v-f5b28690]{padding:20px}.modal-standard .container[data-v-f5b28690]{padding:60px;border-radius:var(--border-radius,4px)}@media screen{[data-color-scheme=dark] .modal-standard .container[data-v-f5b28690]{background:#1d1d1f}}@media screen and (prefers-color-scheme:dark){[data-color-scheme=auto] .modal-standard .container[data-v-f5b28690]{background:#1d1d1f}}@media only screen and (max-width:735px){.modal-standard[data-v-f5b28690]{padding:0;align-items:stretch}.modal-standard .container[data-v-f5b28690]{margin:20px 0 0;padding:50px 30px;flex:1;width:100%;border-bottom-left-radius:0;border-bottom-right-radius:0}}.backdrop[data-v-f5b28690]{overflow:auto;background:rgba(0,0,0,.4);-webkit-overflow-scrolling:touch;width:100%;height:100%;position:fixed}.container[data-v-f5b28690]{margin-left:auto;margin-right:auto;width:980px;background:var(--colors-generic-modal-background,var(--color-generic-modal-background));z-index:1;position:relative;overflow:auto;max-width:100%}@media only screen and (max-width:1250px){.container[data-v-f5b28690]{width:692px}}@media only screen and (max-width:735px){.container[data-v-f5b28690]{width:87.5%}}.close[data-v-f5b28690]{position:absolute;z-index:9999;top:22px;left:22px;width:30px;height:30px;color:#666;cursor:pointer;background:none;border:0;display:flex;align-items:center}.close .close-icon[data-v-f5b28690]{fill:currentColor;width:100%;height:100%}.theme-dark .container[data-v-f5b28690]{background:#000}.theme-dark .container .close[data-v-f5b28690]{color:#b0b0b0}.theme-code .container[data-v-f5b28690]{background-color:var(--background,var(--color-code-background))}