Create public and private networks

[Stretch96]

• This calculates the IP range for the 'private' and 'public' networks within the VPC. It does this by initially splitting the given vpc CIDR block into 2, and then calcalting the 'nebits' so that individual '/24' ranges can be calulated for subnets.
• A subnet for each given availability zone will be created, in both the 'private' and 'public' ranges.
• A public route table will be created, along with an Internet Gateway, and a 0/0 route created for the gateway. The subnets within the 'public' range will then be associated with this route table, allowing any resource launched within them to access the internet.
• A private route table will also be created. If 'public' networking is enabled, a NAT gateway will be created in one of the public subnets, and a route created to allow resources within the 'private' subnets access to the internet.
• Example subnets that will be created:

infrastructure_vpc_cidr_block                 = "10.0.0.0/16"
infrastructure_vpc_network_enable_public      = true
infrastructure_vpc_network_enable_private     = true
infrastructure_vpc_network_availability_zones = ["a", "b", "c"]

public subnets (Allocated "10.0.0.0/17"):
[
  "10.0.0.0/24",
  "10.0.1.0/24",
  "10.0.2.0/24"
]

private subnets (Allocated "10.0.128.0/17"):
[
  "10.0.128.0/24",
  "10.0.129.0/24",
  "10.0.130.0/24"
]

[rjw1]

Could you provide a sample of what the new variables end up outputting. (The plan would be fine possibly)

[Stretch96]

I've added an example to the git comment and PR description 👍