python documentation upgrade

[ofloveandhate]

this pull request represents the addition of Sphinx to PyBertini is its documentation system.

Inspired by GalSim, particularly issue 160, I completely rewrote the way the bindings are structured. its now far more canonical.

• _pybertini is the internal C++ side, raw generated boost bindings
• pybertini is the pure python side, wrapping the generated library into a nice package, with documentation done in sphinx
• you can install the pure python bindings with pip install ., which is cool. before, there wasn't an easy way to install them

additionally,

• there are now two tutorials,
  • one of which loops to track paths to nonsingular endpoints
  • the other constructs and evaluates the cyclic-n system, for n = 10. it's super easy to formulate systems using PyBertini, with programmatic variable creation and convenient ways to loop and define systems with structure.
• i made many improvements to the exposure of multiprecision numbers, and in other places throughout the library
• all tests work again. pybertini needs more testing, but that's always the case, ha.

[ofloveandhate]

i just checked out a fresh copy and everything went smooth, both c++ and python