F/injective-math improvements

[DrunkenRandomWalker]

1. replaced bigint with primitive-types, because bigint is deprecated.
2. improved exp, pow, and ln numerical precision to double precision.
3. added newton's method, discrete_newton's method, halley's method for root finding.

[maxrobot]

Seems like a good step to making the package better but can we:

1. make sure there is a consistent interface

Meaning that all public functions are not underscored, and if they are not to be public the to perform that at the function definition level

Keep mathematical operations like power, exp, sqrt available.

2. Also remove uncommented code

3. There is use of unwrap which I think is unsafe, please make sure we are handling unwraps appropriately.

[DrunkenRandomWalker]

Seems like a good step to making the package better but can we:

1. make sure there is a consistent interface

Meaning that all public functions are not underscored, and if they are not to be public the to perform that at the function definition level

Keep mathematical operations like power, exp, sqrt available.

2. Also remove uncommented code

3. There is use of unwrap which I think is unsafe, please make sure we are handling unwraps appropriately.

1 and 2 are done.

[gorgos]

looks mostly good, although I cant go through the math in detail of course, hopefully the tests and us using the new version will be sufficient

[gorgos]

LGTM