Accept options variables like `111xxx` or `truexxx`

[jcamiel]

Some Options variables are rejected while being "usual":

GET http://localhost:8000
[Options]
variable: foo=aa11
variable: bar=11aa

$ hurl /tmp/test.hurl
error: Parsing literal
  --> /tmp/test.hurl:4:17
   |
 4 | variable: bar=11aa
   |                 ^ expecting 'line_terminator'
   |

And

GET http://localhost:8000
[Options]
variable: foo=true_is_true

$ hurl /tmp/test.hurl
error: Parsing literal
  --> /tmp/test.hurl:3:19
   |
 3 | variable: foo=true_is_true
   |                   ^ expecting 'line_terminator'
   |

[jcamiel]

@fabricereix I think it's reasonable that these two Hurl snippets work (without quoting the variable value to force the string type)