Type input variables

[fabricereix]

Values used in Hurl in Captures/Assert are typed (integer, boolean, string,...)
On the opposite, the input variables (from the option --variable) are all strings.

sample.hurl 
 1  GET http://localhost:8000/hello
 2  HTTP/* 200
 3  [Asserts]
 4  variable "count" equals "1"
 5  variable "count" equals 1

$ hurl --variable count=1 sample.hurl 
error: Assert Failure
  --> /tmp/sample.hurl:5:0
   |
 5 | variable "count" equals 1
   |   actual:   string <1>
   |   expected: int <1>
   |

It will be interesting to type the input variable implicitly.
The string <1> should be treated as integer, therefore the first assert should fail rather than the second.

Similarly, the value should be treated as bool.
To force a string value, the value can be quoted.
This is consistent with the predicate value.

For example, the id <123> is passed as string as follow:

hurl --variable id='"123"' sample.hurl 

[fabricereix]

implemented in #176