Release notes for v0.5.0

Changes by Kind

Grammar: rename rules:
- expr to literal-expr
- expr2 to expr (#93, @vgramer)
Remove references to old repo vgramer/opa-idea-plugin. The repository has been transferred to open-policy-agent organization (#83, @vgramer)

Grammar: allow factor expression (ie parenthesis ). These expressions were passed as an error:
- a4:= (1 - 3) - (2 +5)
- reverse(l) = [l[j] | _ = l[i]; j := (count(l) - 1) - i] (#92, @vgramer)
Grammar: allow complex expression as array index. These expressions were parsed as an error:
- x:= x[minus(count(x),1)]
- index_last(l, x) = t[minus(count(t), 1)] { #something} else = -1 { # something}
- rule1{ x:= x[count(x) - 1)] } (#91, @vgramer)
Grammar: allow complex expression for array and object value. these expressions were parsed as an error:
- arr7 := [1 + 2 - 4, count(arr6) / abs(arr5[0])
- a6 := { a: 1 > 2, b: { c: object.get(a2, a, default) + abs(c) - 2 }} (#90, @vgramer)
Grammar: allow empty query in else clause. These expressions were reported as an error
- foo = true { input.x < input.y } else = false
- foo = true { false } else = { true } (#85, @vgramer)