Support several more numerical operations.

[wmedrano]

After this PR:

Implemented

• -
• *
• +
• /
• abs
• ceiling
• denominator
• expt
• floor
• numerator
• quotient
• round
• square
• number?
• complex?
• real?
• rational?
• integer? - r7rs specifies that (integer? 7.0) should return #t, Steel returns #f.
• exact-integer?
• exact?
• inexact?
• finite?
• infinite?
• odd?
• even?
• number->string
• string->number
• exact->inexact
• inexact -> exact

Pending

• exact-integer-sqrt
• floor/
• floor-quotient
• floor-remainder
• gcd
• lcm
• max
• min
• modulo
• rationalize
• remainder
• truncate
• truncate/
• truncate-quotient
• truncate-remainder
• nan?
• zero?
• positive?
• negative?
• sqrt
• make-rectangular
• make-polar
• real-part
• imag-part
• magnitude
• angle
• inexact
• exact

[mattwparas]

Ready for review?

[wmedrano]

Ready for review.

[mattwparas]

Thanks!