Add I/O redirection to Unix trail
Add Free/$ to Heroku and GitHub
[#45] Remove link to CoffeeScript stub trail
[#4] Create Open Source trail

* Link to Dr. Nic's classic 8 steps article.
* Link to SemVer.
* Separate using open source, contributing open source, and maintaining
  an open source project.
* Promote NEWS and ChangeLog files.
* Promote SemVer.
Add @include and @extend to Sass trail
Add ongoing reference section to Open Source trail

Include choice morsels from "The Architecture of Open Source
Applications."
[#23] Create Javascript trail
Link to Javascript trail from README
[#46] Delete Coffeescript trail

No stubs in master. It's disappointing as a reader.
[#38] Add Rails Core mailing list as reference
Add intermediate section and link items
Add some links to advanced git
Corrected Contributing Guidelines link
Add thoughtbot style guide
Fix link for style guide
Add Semantic Versioning link

* Also link rubygems and github
Update GitHub Links

- Added main "Get GitHub" link with ($/free)
- Linked other mentions of GitHub - no $/free needed since it's at the top of the trail
- Also linked other sites mentioned
Update style guides

* Add community driven Ruby style guide.
* Add Ruby style guide.
* Add GitHub Ruby style guide.
Use new edition of Learn Objective-C on the Mac
[#49] Start design trails

* Start grids trail
* Start typography trail.
* Start visual design trail.
* Start information design trail.