Signature v4
Always include update action - required by DynamoDB Local
SecurityToken support
Fix base16 to handle leading 0
Merge pull request #49 from talko/sigv4

Implement AWS signature v4 and use for erlcloud_ddb
Upping API version used by erlcloud_ec2:describe_instances and exposed an API to specify request parameters (i.e. to allow use of request filters for example
Support launching images with multiple security groups
Implemented erlcloud_aws:param_list_r in an effort to provide some clarity and a function that is able to build arbitrarily nested parameter lists. This will be needed for things like creating EC2 instances with multiple interfaces on different security groups, etc.
Checkpointing creation and modification of network interfaces
Some more changes to get EC2 instance creation with multiple interfaces working
Added interface to Route53 API
Added support for all actions on hosted zones
Added actions on resource record sets for Route53 API
a couple of fixes to get get_record_set working more like one would expect
use newer API to allocate public IP on non default subnet
merging support for signature 4