Throw Exceptions for Request Errors

[bartboy011]

This PR introduces threw new exception classes:

• TimeoutException (cURL timeout)
• ClientException (4** responses)
• ServerException (5** responses)

Each exception contains the appropriate error message (ie, cURL's error or the response error) as well as the returned status code as the exception's code (except for TimeoutException).

All three exceptions extend the RequestException class, which extends the base \Exception class.

Additionally, this PR adds a cURL connection timeout of 10 seconds.

cc: @mthommes @cristiangrama

[bartboy011]

@ActiveCampaign/integration

[bartboy011]

@mthommes Updated!

Edit: also @cristiangrama

[bartboy011]

@cristiangrama Looks like you don't get assigned after approval on this repo yet

[bartboy011]

Also, @mthommes to answer your question about the major version, yes, the next few PRs I'll be opening will all be part of v3