* Issue #56: Added tags for elastic ips

* add cidr_block outputs to public and private subnets

* add cidr_block outputs to database and elasticache subnets

* add redshift subnet option

* fix tag

* add missing route association for redshift

* add vpc_endpoint_s3_pl_id and vpc_endpoint_dynamodb_pl_id outputs

* add redshift to complete-vcp example

* fix domain_name_servers - keep it a list

* fix outputs for TF 0.11

* fix missing *

* Minor corrections in example and in type of dhcp_options_domain_name_servers

* Minor corrections in example

* Updated README

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I want to add a badge to the README of this project. The idea is to
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- https://github.com/crystal-lang/crystal
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* Added fix for issue when no private subnets are defined

* Minor readme

* Allow passing in EIPs for the NAT Gateways

* Document how to pass external IPs for NAT Gateways

* Update README.md to reduce example code

Outputs directly referencing resource IDs that are only conditionally
created are not valid. Use the concat * trick to make sure we always
have a valid value for these outputs.

* Add support for DHCP options set

* code cleanup

* remove unnecessary depends_on in aws_vpc_dhcp_options_association definition

Add AZ to nat gateway name

NAT gateway should be tagged too.

Improve variable descriptions

disable dynamodb data source when not needed

Allow the user to define custom tags for route tables