remove md5 checksum support

Following up on #2719.  MD5 checksums are
* nowhere mentioned in our docs
* not used in any existing Cask
* deprecated in Homebrew
Therefore it seems sensible to delete this code.
Added OpenSesame

OpenSesame is a graphical, open-source experiment builder for the
social sciences. It sports a modern and intuitive user interface that
allows you to build complex experiments with a minimum of effort. With
OpenSesame you can create a wide range of experiments. The plug-in
framework and Python scripting allow you to incorporate external
devices, such as eye trackers, response boxes, and parallel port
devices, into your experiment.
move HACKING.md and CHANGELOG.md to doc subdir
doc: remind to upgrade before filing bug report
more reliable way to look up username

`ENV` is manipulable.  `getpwuid` is reliable.
LibreOffice 4.2.1
Merge pull request #3077 from ndr-qef/libreoffice

LibreOffice 4.2.1
add files_in_usr_local caveat to several Casks
Merge pull request #3022 from alebcay/opensesame

Added OpenSesame
Add Golly 2.6

Cellular automata editor with a focus on Conway's Game of Life.
mauve 2.3.1: New formula

Multiple Genome Alignment Visualization
http://gel.ahabs.wisc.edu/mauve/

Mauve is a system for efficiently constructing multiple genome
alignments in the presence of large-scale evolutionary events such as
rearrangement and inversion.
Merge pull request #3081 from ndr-qef/golly

Add Golly 2.6
Merge pull request #3082 from sjackman/mauve

mauve 2.3.1: New formula
Merge pull request #3067 from rolandwalker/organize_docs

move HACKING.md and CHANGELOG.md to doc subdir
Merge pull request #3080 from rolandwalker/add_local_caveat

add files_in_usr_local caveat to several Casks
Merge pull request #3074 from rolandwalker/doc_bug_report

doc: remind to upgrade before filing bug report
VLC 2.1.4
Merge pull request #3088 from ahbeng/vlc

VLC 2.1.4
Update Widelands to Build 18
Add (unoffical) Google Music app v1.0.2