Refactor: a new httpclient

[breezewish]

This PR provides a new design of the HTTP client, pretty much close to resty.

Primary advantages:

• No need to call Close(), just like resty.
• No need to process error multiple times during the calling, just like resty, one chained call for all.
• Unlike resty, No need to call and pair SetDoNotParseResponse() + .RawResponse in order to do streaming, just call PipeBody().
• Unlike resty, No need to call and pair SetResult(&Foo{}) + .Result().(*Foo) in order to unmarshal, just call ReadBodyAsJSON(&foo).

Sample usages below :

Get response body in bytes:

bytes, _, err := httpclient.New(httpclient.Config{}).LR().
    Get(....).
    ReadBodyAsBytes(&data)
if err != nil {
    // error handling
}

Unmarshal JSON:

var data FooResponse
_, err := httpclient.New(httpclient.Config{}).LR().
    Get(....).
    ReadBodyAsJSON(&data)
if err != nil {
    // error handling
}

Streaming:

writtenBytes, _, err := httpclient.New(httpclient.Config{}).LR().
    Get(....).
    PipeBody(someWriter)
if err != nil {
    // error handling
}

Set Headers:

var data FooResponse
_, err := httpclient.New(httpclient.Config{}).LR().
    SetHeader("x-requested-with", "foo").
    Get(....).
    ReadBodyAsJSON(&data)
if err != nil {
    // error handling
}

Reuse clients:

client := httpclient.New(httpclient.Config{})
_, _, _ = client.LR().Get(...).ReadBodyAsString()
_, _, _ = client.LR().Get(...).ReadBodyAsString()

Read response headers:

bytes, rawResp, err := httpclient.New(httpclient.Config{}).LR().
    Get(....).
    ReadBodyAsBytes(&data)
if err != nil {
    // error handling
}
fmt.Println(rawResp.Header.Get("x-header"))

[ti-chi-bot]

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• shhdgit

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[shhdgit]

knowledge++++

[shhdgit]

Maybe it's too surprising to have TrimSpace, as a common http client.

[breezewish]

This behavior is taken from resty:

// String method returns the body of the server response as String.
func (r *Response) String() string {
	if r.body == nil {
		return ""
	}
	return strings.TrimSpace(string(r.body))
}

[breezewish]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 1c9f041