explicitly disabling sci & sci options, fixes #276

[ikitommi]

Option 2 for #276. A non-breaking change (opposed to option1).

Disabling sci:

(m/validate [:fn 'int?] 1)
; => true

(m/validate [:fn 'int?] 1 {::m/disable-sci true})
; Execution error
; :malli.core/sci-not-available {:code int?}

Custom sci options:

(m/validate [:fn '(fn [x] (< x (last (range 10))))] 1)
; => true

(m/validate [:fn '(fn [x] (< x (last (range 10))))] 1 {::m/sci-options {:realize-max 1}})
; => false

[miikka]

Doing this still keeps the door open for a breaking change