Add improvements for links

This PR brings minor improvements for the links listed throughout this repository:

All links that support HTTPS have https:// instead of http:// (this is a cryptography library, after all!) with the exception of the link in LICENSE.md which stays at http:// to remain consistent with the license format on unlicense.org
All mentions of GitHub users now have links (for instance, @dchest would now be @dchest)
Standalone links have been shortened through hiding the https:// portion (for instance, https://dchest.github.io/tweetnacl-js/ would now be dchest.github.io/tweetnacl-js/)
Some links which now redirect to slightly different URLs have been updated with the new redirected URL
Link placements in AUTHORS.md have been updated so that the format is consistent

I dedicate any and all copyright interest in this software to the
public domain. I make this dedication for the benefit of the public at
large and to the detriment of my heirs and successors. I intend this
dedication to be an overt act of relinquishment in perpetuity of all
present and future rights to this software under copyright law.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

dchest / tweetnacl-js

Add improvements for links #234