Fix AWS credential params for s3 and other modules

The `ec2_ami`, `ec2_elb`, `ec2_tag`, `ec2_vpc`, `route53`, and `s3` modules
all canonicalize the AWS access and secret key params as
`aws_access_key` and `aws_secret_key`. However, following the fixes for #4540,
those modules now use `get_ec2_creds` from `lib/ansible/module_utils/ec2.py`,
which requires access/secret key params to be canonicalized as
`ec2_access_key` and `ec2_secret_key`. As a result, AWS credentials passed
to those six modules as parameters are ignored (they instead always use
the AWS credentials specified via environment variables, or nothing).

So this change fixes those six modules to canonicalize the
AWS access and secret key params as `ec2_access_key` and `ec2_secret_key`,
allowing them to again accept AWS credentials passed via module params.
fixed documentation typo about region purpose
Merge pull request #5068 from jimrybarski/devel

fixed documentation typo about region purpose
Merge pull request #5067 from justinludwig/fix-aws-credential-params

Fix AWS credential params for ec2_ami, ec2_elb, ec2_tag, ec2_vpc, route53, and s3 modules
Fix accelerate module parameter for IPv6 activation
Fix bug in error detection code, where a zero-length string was causing a traceback

Fixes #5064
Fixes #5056 Append new hosts to the groups cache
fix heading name syntax in AWS guide
Avoid a traceback when using accelerate

This bit of code is attempting to access accelerate_inventory_host,
which may not have been set/created. This will cause a traceback.
Instead use getattr with a fallback to False.
Fixes #5030 compare connection user and sudo user and disable sudo if identical
Merge pull request #5085 from tgerla/awsfixes

fix heading name syntax in AWS guide
Merge pull request #5086 from j2sol/fix-accelerate_inventory

Avoid a traceback when using accelerate
Add release history for 1.4.1 into 1.5 branch.
Correct the invocation of ‘_assemble_from_fragments’
Docs: Fix the module formatter code that is intended to remove the 'historical' variable from showing up in version_added information (RST)
No longer need to reference 'version_added' in docs for these, as this was quite a while ago.
There's a cleaner way to do this, commit to module formatter pending.

Revert "No longer need to reference 'version_added' in docs for these, as this was quite a while ago."

This reverts commit ff0a41d446a03f93aa57a6baa96c5333bea269ea.
Code to limit display of version_added attributions in modules for modules that are too old to call out this information.

This does not generically apply to new arguments added to existing modules, just the version_added attribute on the top level modules.
Update the .gitignore based on the docsite restructuring.
Merge pull request #5088 from EspadaV8/5057_assemble_fix

Correct the invocation of ‘_assemble_from_fragments’