cygwin setup 2.830 properly handles dependencies now (version 2)

Changelog:

Removed package dependencies, as Cygwin setup 2.830 no longer requires them to be listed.
Changed mirror to http://mirrors.kernel.org/sourceware/cygwin/ for speed.
Replaced hardcoded C: drive references with %SYSTEMDRIVE%.
Hardcoded architecture to "x86" as "x86_64" seems a bit buggy still.
Changed temporary directory from C:\WINDOWS\temp to %TEMP%.
Added additional comments

I tested these changes, and the boxes

win2008r2-datacenter
win2008r2-enterprise
win2008r2-standard
win2008r2-web
win2012-standard
win2012r2-standard
win7x64-enterprise
win7x64-pro
win7x86-enterprise
win7x86-pro
win81x64-enterprise
win81x64-pro
win8x64-enterprise
win8x86-enterprise

successfully install OpenSSH, and VMWare Tools.

The boxes

win81x86-enterprise
win81x86-pro

fail to build as the default `e1000` network adapter doesn't work. This will be fixed in another PR.

The boxes

win2012-datacenter
win2012r2-datacenter

can't be built, as the sshd service logs the following error when it's started:

`sshd pid service sshd failed signal 11 raised`