Add Network interfaces per Region limit

[nadlerjessie]

Summary

This PR adds the Network interfaces per Region limit. This limit is described here is a bit unusual because the default is:

This limit is the greater of either the default limit (350) or your On-Demand Instance limit multiplied by 5.

I used 350 because that is the initial limit a new account will have, given that the default limit for On-Demand Instances is 20.

I had some trouble getting the docs to build so I did not complete that step (it is the only failure in travis). Sorry about that!

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[jantman]

Thanks so much! And thanks for adding the tests as well!

No worries about the docs build, they're rebuilt as part of the release process anyway.

I have a pretty busy week this week, so I might not be able to get this reviewed, merged, and released until the weekend, but I'll do my best.

@nadlerjessie Just a thought regarding the weird "greater of either the default limit (350) or your On-Demand Instance limit multiplied by 5." calculation for this limit... the DescribeAccountAttributes EC2 API call returns, among other things, the account's current Running On-Demand EC2 Instances limit in the current region. awslimitchecker is already using that to dynamically update the Running On-Demand EC2 limit in _Ec2Service._update_limits_from_api().

Would you have anything wrong with me (or you, if you want) adding some logic to that _update_limits_from_api() method to update this new Network Interfaces limit, based on the formula and the On-Demand Instance limit data?

[nadlerjessie]

I like that idea, I didn't know about _update_limits_from_api! I'll take care of it. And no rush on the release, thanks for letting me know.

[jantman]

Ok, thanks so much!

Yeah, unfortunately EC2 exposes very few of the limits via DescribeAccountAttributes...

[codecov-io]

Codecov Report

Merging #379 into develop will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           develop   #379   +/-   ##
======================================
  Coverage      100%   100%           
======================================
  Files           30     30           
  Lines         2256   2261    +5     
  Branches       335    335           
======================================
+ Hits          2256   2261    +5

Impacted Files	Coverage Δ
awslimitchecker/services/vpc.py	100% <100%> (ø)	⬆️

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[jantman]

This looks great, thanks so much again!

[jantman]

The only build failure was a broken link found by the docs build. Merging now; I'll clean that up before release

[jantman]

@nadlerjessie By the way, I just wanted to say thank you for submitting such a well-done PR. It's rare on small projects like this that people take the time to go through the PR template, provide a good summary, tests, etc. It's greatly appreciated.

[nadlerjessie]

You're welcome @jantman! Thanks for maintaining such a great library and for the quick review

[jantman]

This has been released as 6.1.0 and is live on PyPI. Thanks again!