Removed 'static bound requirements for the lambda_http crate and create a shared resources example for the crate

[coltonweaver]

Following discussion in #310, it makes sense to include these changes in the lambda_http crate as well. I've given this work a pass, and am looking for feedback now.

Issue #, if available: #310

Description of changes:

• Added explicit lifetime bounds on each of the handler and adaptor types in the lambda_http crate, so we don't have to rely on the futures for these being 'static any longer.
• Added an example of how one might use this to the examples folder. Have tested that these changes work in the Lambda console with an APIGW event:

Response
{
  "statusCode": 200,
  "headers": {},
  "multiValueHeaders": {},
  "body": "f9b73b61-82cf-4da5-b084-19f01ee76346: Client (random_client_name_1) invoked by Colton.",
  "isBase64Encoded": false
}

The request was a regular APIGW proxy event with the query string value "first_name" set to my name.

By submitting this pull request

• [ X] I confirm that my contribution is made under the terms of the Apache 2.0 license.
• [ X] I confirm that I've made a best effort attempt to update all relevant documentation.

[bahildebrand]

Can you give more context on what this is for? I'm not sure I understand.

[coltonweaver]

Sure, if you look down below it's because I added the explicit lifetime to the Adapter struct, because it holds a Handler that requires a lifetime parameter. Because the 'a lifetime is unused in Adapter, otherwise, the compiler complains about the unused lifetime parameter we supplied to it. The PhantomData is just a zero-sized compiler dummy value that holds the 'a lifetime and "uses" the lifetime to make the compiler happy.

[bahildebrand]

Ah, okay. That makes sense now thank you.