Add Visual Studio 2010 SP1 download URL

Many people are confused by indicating just Visual Studio 2010 Express without SP1
:memo: Unify the two contributing documents

Both documents had some really great stuff to them, but there was too much
overlap. I did my best to unify them into one document, taking the best
features of each.
Use Atom-specific fork of React allowing selection restoration opt out

This fork of React allows data-react-skip-selection-restoration to be
defined on input elements, skipping costly selection restoration that
occurs when the input element is focused during reconciliation.
Use 'with' instead of 'and'

Using 'with' instead of 'and' could prevent some people to think that SP1 is an other program, or is Windows SP1
Remove unused sync option
Upgrade to bracket-matcher@0.38.0
Split out the package-specific information

Per PR feedback, splitting out package-specific development information
into its own document.
Merge pull request #2295 from lee-dohm/contributing

:memo: Unify the two contributing documents
Add spec documentation
Add links to writing specs doc
Call hide on the views instead of the jQuery collection

This ensures that views with custom ::hide methods can invoke special
behavior.
Don't measure lineHeight/defaultCharWidth when editor is hidden
Avoid measuring lineHeight/defaultCharWidth on show unless needed

We only need to re-measure if the fontSize, fontFamily, or lineHeight
changed while the editor was hidden.
Ensure .lines div is always at least the height of the scroll view

This ensures that the wrap guide extends the entire height of the
editor.
Updates Jasmine link in CONTRIBUTING.md
Merge pull request #2353 from aaronraimist/master

Updates Jasmine link in CONTRIBUTING.md
added a solution for an issue in linux troubleshooting section
Merge branch 'master' of https://github.com/klorenz/atom
Merge pull request #2339 from atom/cj-add-spec-documentation

Add spec documentation
Rename lineHeight to lineHeightInPixels to distinguish from CSS value

CSS has a line-height property with values like '1.3', but we also have
a measured pixel value for line height. It's important to keep these
separate conceptually.