Add a conventions document.

This will contain the style guide (once it's written) and presently
contains the beginnings of a standard example network. The diagram still
needs some work, but all of the important machines are present.
Expand on shell portability concerns

- Explain the difference between /bin/bash, /bin/sh, and /usr/bin/env bash when specifying an interpreter for a shell script.
Wrap string literals per review comments,
Explain what the hashbang is and why it's important
Make bash manual a link, rather than have the link floating off in space.
Update package_management_101.rst
Attempt to address outstanding review comments.  (typos hopefully all fixed now).
Merge branch 'master' of https://github.com/sdaugherty/curriculum into sdaugherty-master
programming_101: typo fixes, term creation for glossary
Added guidelines
Adds links to references
Merge pull request #116 from miketheman/guidelines

Added guidelines
removed extra word.

@avleen should have caught that in his review :stuck_out_tongue:
This file shouldn't have execute bit set.
Merge pull request #120 from sdaugherty/permfix

This file (netbooting.rst) shouldn't have execute bit set.
Update sysadmin_101.rst

Improve some awkward phrasing/grammar
Update sysadmin_101.rst

Improve awkward phrasing
Update filesystems_101.rst

Correct misspelling.
Update package_management_101.rst

Correct misspellings. Comment about dependency resolution. Remove extraneous apostrophe. Insert omitted words.
Merge pull request #123 from dhutty/master

Correct some misspellings and the like. Minor rewordings.