Issue #29 Added describeLead rest end point to the library

[ghost]

Please review changes added as part of issue #29.

Thank you.

[Jaesin]

This is also in #34 but by a different name getFields. Is describeLead more desirable?

[ghost]

Due to the snail pace on PR approvals with this project we were forced to use a forked local branch on our platform. I intend to periodically check back and merge new features into our local repo.

[itmayziii]

@Jaesin In this case getFields to me would be more desirable with some tweaking to how it was implemented in #34.

Currently the getFields method only supports leads. In fact this whole repository only supports Leads. With the idea of expanding this client to support companies and opportunities we should think of how we want to move forward with naming.

Here are the options in my opinion.

Option 1:
Have a separate function call for each object in Marketo.

1. describeLeads
2. describeCompanies
   3 describeOpportunities

OR...

Option 2:
Have 1 method call that takes the object name as a parameter
describeObject($objectName) or getFields($objectName)
Marketo uses the word "describe" so it seems to make sense to name our functions that way.

If you really want to have the method names describe what is happening then you could just wrap the general describeObject call with your named function

describeLeads() { return $this->describeObject('Leads'); }

That way you still have all the code being reused with describeObject but you get the nice method name as well. Just my thoughts, I plan on contributing to this repo soon with functionality to support companies and opportunities so I wanted some others opinions on how to move forward.

@dchesterton Any thoughts?