Add taut string gating code

[gfinak]

@mikejiang Could you perform code review? I've rebuilt the docs with roxygen and I'm concerned why it edited existing documentation. There's C++ code for the taut string density estimator gating from Evan and a wrapper to implement it as an opencyto supported method.

[mikejiang]

The reason of editing/adding docs for existing functions are caused by the latest changes from roxygen2 6.1.0

• Objects with names starting with a dot are now by default documented in files with prefix ‘dot-’.
• string_wrap seems to use the shorter max length now The suppress doc-generating for these internal function, I will have to add @noRd tag explicitly to each of them. Too bad that roxygenize doesn't provide an option to keep the behavior backward consistent :(