Allow user to specify tolerance for `locate`

[Darylgolden]

It would be helpful if the user can specify the tolerance for whether a slightly offset point would be considered on the curve.

[dhermes]

Relevant lines to make this happen:

• https://github.com/dhermes/bezier/blob/e6925aad702842ae3637dfac9ff0da556ef0d980/src/python/bezier/hazmat/curve_helpers.py#L894
• https://github.com/dhermes/bezier/blob/e6925aad702842ae3637dfac9ff0da556ef0d980/src/python/bezier/hazmat/curve_helpers.py#L883 (would need to add a buffer)
• https://github.com/dhermes/bezier/blob/e6925aad702842ae3637dfac9ff0da556ef0d980/src/fortran/curve.f90#L547