feat(siu): allow pipe func to accept args and kwargs

[machow]

This PR expands the pipe function, and adds a call() function, to allow...

• pipe() for a manual version of making pipes w/ >>
• call() for making a specific step of pipe
  • arbitrary *args and **kwargs
  • a siu expression allowed as the first argument, rather than a regular callable
  • the ability choose where the data should go in the call
• Pipeable() is now deprecated.

Note that this means that the old pipe() was essentially renamed call(). Because pipe() had very limited behavior, these changes are fully backwards compatible.

Should address #246 #408 #207. See #47 for a docs related issue.

⚠️ TODO: Note that I still need to add support for things like call(mutate, _, a = _.x + 1). Going to release as-is, though, since functions like mutate can already be used in a pipe..!

Examples from call docstring

The simplest use of call is passing just the to-be-called function.

s = "a string"
s >> call(print)
# a string

This is equivalent to explicitly passing _ as a placeholder.

from siuba import _
s >> call(print, _)
# a string

The explicit syntax is useful, because it allows us to pass more arguments.
For example, the code below passes additional arguments to print.

"a" >> call(print, _, "string", sep=" ")
# a string

You can transform the input data. For example, the code below passes "shout".upper()
to print.

"shout" >> call(print, _.upper())
# SHOUT

Since _ is just a placeholder for the data on the left-hand-side of >>, you
can pass it multiple times to the to-be-called function (e.g. print).

"nice" >> call(print, _, _, sep=" ")
# nice nice

Alternatively, you can pass a siu expression straight to call.

"abc" >> call(_[0].upper())
# 'A'