Implement Functional Options

[italolelis]

Hello,

As proposed in here #31, the following implements functional options into the library. This is a breaking change and should probably increase the major version. A few things to consider:

New package names

Why?

I started to have name conflicts with the options that were common to both clients since both of them are in the root folder of the project. Here is an example of the issue:

httpClient := heimdall.NewHTTPClient(
	heimdall.WithHTTPTimeout(10), 
	heimdall.WithRetryCount(4),
)

hystrixClient := heimdall.NewHystrixHTTPClient(
	heimdall.WithHTTPTimeout(10), // This name cannot be the same
	heimdall.WithRetryCount(4),// This name cannot be the same
	heimdall.WithHystrixTimeout(1100),
)

For this reason, I thought it would be more elegant to have the client implementations in their own package. I called them httpclient (to avoid conflict with the http package) and hystrix

Now the usage looks like:

	httpClient := httpclient.NewClient(
		httpclient.WithHTTPTimeout(timeout),
		httpclient.WithRetryCount(2),
	)

	hystrixClient := hystrix.NewClient(
		hystrix.WithHTTPTimeout(timeout),
		hystrix.WithCommandName("MyCommand"),
		hystrix.WithHystrixTimeout(1100),
		hystrix.WithMaxConcurrentRequests(100),
		hystrix.WithErrorPercentThreshold(25),
		hystrix.WithSleepWindow(10),
		hystrix.WithRequestVolumeThreshold(10),
	)

Returning concrete types

Now I started to return concrete types on the constructors of the clients and to make sure the compiler can identify if we are implementing the interface I added this line.

var _ heimdall.Client = (*Client)(nil)

If you don't like the packaging strategy please let me know and we can try to find a solution.

Thanks!

[rShetty]

@italolelis Thanks for the PR. will Check it this week.

[rShetty]

@italolelis There are merge conflicts, can you help resolve these plz.

[italolelis]

@rShetty done

[rafaeljesus]

looking forward to this merge, good job @italolelis

[rShetty]

@italolelis Skimmed through the PR. Overall looks solid and Thank you for this. Have added few comments.

[italolelis]

@rShetty Thanks for reviewing, I can't see the comments that you left though. Do I need to fix something?

[rShetty]

Changes

[rShetty]

Brackets seem off, can we fix this

[rShetty]

Can we add some sane defaults to all of the functional options ?

[rShetty]

Defaults in these functional options too

[rShetty]

Maybe also test cases for this file ?

[rShetty]

@italolelis Have commented

[italolelis]

@rShetty I've added the defaults and tests. Please, check if it makes sense.

[rShetty]

Thank you very much for the PR