Update unit tests to be 1.0 compatible
/Cluster/Nodes endpoints should extend a base, abstract class

All endpoints use a NodeID, extending from an abstract class minimizes code
copy/paste
/Indices/Warmer/Get should throw exception on bad argument combination

If `index` and `type` are specified but not `name`, an exception
should be thrown sinc this is an illegal combination.  Valid
combinations are:

"/_warmer", "/{index}/_warmer", "/{index}/_warmer/{name}", "/_warmer/{name}", "/{index}/{type}/_warmer/{name}"
If `type` is specified but not `index`, default to _all

These endpoints should use the `_all` special index if a type is
specified but no index.
[Docs] Add minimum PHP version requirement to Readme