Add predicates to test value types

[fabricereix]

Add the predicates isInteger, isFloat, isBoolean, isString, isCollection

for example, for the following json response

{
    "count": 4,
}

The following asserts fails

jsonpath "$.count" isString
jsonpath "$.count" isFloat

while the following assert is successful
jsonpath "$.count" isInteger

[fabricereix]

implemented in #98