Enhance P and Pf functions to accept multiple arguments, treated as a logical AND

[Pierre Denis]

It would be convenient that P and Pf functions accept multiple arguments, treated as a logical AND:

d = interval(1, 6, 'r')
P(2 <= d, d <= 5)
# -> 2/3 

Rationale: this is consistent with the handling of the arguments of the given method and this would simplify the writing of conjunctions:

P((2 <= d) & (d <= 5)) 

[Pierre Denis]

Enhance P and Pf functions to accept multiple arguments (refs #89)

→ <<cset 205039dffcb3>>

[Pierre Denis]

Minor improvements (refs #89)

→ <<cset 894198ba0a40>>