Adding the ability to specify a security_group_id for the amazonebs builder
builder/digitalocean: use detected env variables for credentials
Add AWS instance id to normal output

The AWS instance id is only output when logging is occurring. If an
error happens it is useful to know the AWS instance id of the instance
spun up by packer in case further cleanup or forensics are needed.
Merge pull request #170 from markpeek/markpeek-awsinstancedebugging

builder/amazonebs: Add AWS instance id to normal output
Validate that instance exists and is EBS based before trying to launch it.
Merge pull request #172 from MattSurabian/feature/ebs-builder-bug

builder/amazonebs: Validate that instance exists and is EBS based before trying to launch it
Update CHANGELOG
fmt
Add support for -force flag on builds [GH-119]
builder/digitalocean: add tests for credentials via env vars
Merge pull request #164 from mitchellh/do-env-vars

builder/digitalocean: use detected env variables for credentials
Update CHANGELOG
Merge pull request #162 from brendanhay/persistent-security-group

builder/amazonebs: Ability to specify a pre-existing SecurityGroupId for the AmazonEBS Builder
website: add docs for new security_group_id
Add instructions for how to get Go set up to contribute.
Merge pull request #173 from jasonberanek/force-build

packer, builder/*: Add support for -force flag on builds [GH-119]
Update CHANGELOG
fmt
Merge pull request #176 from smerrill/better-contributor-notes

Add instructions on how to get Go set up to contribute.
Remove output directory in a step when "-force" flag step [GH-178]