Support arithmetics with YAQL expressions

Support basic arithmetic operations (*/+-) and operator precedence in YAQL expressions (i.e. (1+2) * 3 vs. 1 + 2 * 3).

EXAMPLES:

version: "2.0"
wf1:
  type: "direct"
  input:
    - a
    - b
    - c
  tasks:
    t1:
       action: ... d={$.a + $.b + $.c}

AND

version: "2.0"
wf1:
  type: "direct"
  input:
    - a
    - b
    - c
  tasks:
    t1:
       action: ... d={($.a + $.b) + $.c}