Backslash escape required for links with parentheses

Also fixes up some malformed links to Git SCM and Pro Git book sites.
Merge pull request #71 from randomecho/link-plink

Backslash escape required for links with parentheses
Pare Contributing to action call; Markdown H1 format consistency

CONTRIBUTING could just do with being about what to contribute
and how to help the materials instead of repeating what is
already found in the README with the license and rep summary.
Merge pull request #72 from randomecho/contributing-meat-slice

Pare Contributing to action call; Markdown H1 format consistency
Format transcript to improve readability

Proof of visual concept to see how things would look if we only had
lines of the transcript that went no farther than 125 and aligned
the names and messages in a way to more easily track who typed what.
Notes for private class
Fixed title in private class notes
Git and GitHub in the life sciences
updated link to altmetrics page for my article
Merge pull request #75 from karthikram/gh-pages

Updated link to social media response
First draft of chatops presentation outline
Merge pull request #73 from randomecho/transcript-alignment

Format transcript to improve readability by separating users and messages
Fixed typos
Merge pull request #77 from pborreli/typos

Fixed typos
SIGCSE outline
Added HydeSlides Plugins submodule for initial inclusion of Table of Contents feature
Merge pull request #78 from github/hydeslides-update

Added HydeSlides Plugins submodule for initial T of C feature
make path to presentations/plugins submodule relative so git can properly detect it
Add rdiscount and RedCloth to Gemfile

`bin/build` fails without them.

Also s/:rubygems/https://rubygems.org to prevent deprecation warning when bundler fires.
Corrected submodule path for presentations/, accidental absolute pathing from dev box