Reorganization, rephrasing, addressed a lot of issues (jaywcjlove#336)

* Migrated RSS to a standalone section

* Swapped CMD markdown for Marxico, crunched FTP into File Sharing, added "plugin" description to Jetbrains Plugins, added OSS links

* Added ygraph, beardedspice, fixed spelling and spacing

* Split General Tools into subsections and added to TOC

* Replaced ttygif with asciinema

* Intro phrasing, removed KOffice because I couldn't find a Mac port of it. It seems to be a Linux distribution only

* Broke Test Tools into more specific categories, fixed phrasing

* Added PULL_REQUEST_TEMPLATE in docs dir

* Added ISSUE_TEMPLATE in docs dir

* Updated CONTRIBUTING.md