Close #69 Unused Var: Warning

Fix #75 <complex> may define macro I

Fix #75 as described by undefining the macro `I` from `<complex>`
if defined (as in `glibc`).

This seems to be the only include of it.

Close #69
[This](http://stackoverflow.com/a/3418951)
stackoverflow post recommended
[that](http://herbsutter.com/2009/10/18/mailbag-shutting-up-compiler-warnings/)
Herb Sutter blog post with a general and portable solution and it
works great! :)

Fix Compile Error: str Naming

This fixes a build error compiling with `nvcc/7.5` + `gcc/4.9.2`
causing a
```
./include/pybind11/pybind11.h(952): here

./include/pybind11/pytypes.h: In member function ‘pybind11::str pybind11::handle::str() const’:
./include/pybind11/pytypes.h:269:8: error: expected primary-expression before ‘class’
     return pybind11::str(str, false);
        ^
./include/pybind11/pytypes.h:269:8: error: expected ‘;’ before ‘class’
./include/pybind11/pytypes.h:269:8: error: expected primary-expression before ‘class’
```

- new pybind11::base<> attribute to indicate a subclass relationship
- unified infrastructure for parsing variadic arguments in class_ and cpp_function
- use 'handle' and 'object' more consistently everywhere

fixed a terrible bug in def_property_static and switched to the faster PyObject_CallFunctionObjArgs API call

fully moved __pybind11__ Python attributes to the C++ side, cleanup & documentation pass over the main header file

moved lifetime management of Py_buffer to pybind11::buffer_info, renamed count->size to match NumPy naming (fixes #34)

Previously, pybind11 required classes using std::shared_ptr<> to derive
from std::enable_shared_from_this<> (or compilation failures would ensue).

Everything now also works for classes that don't do this, assuming that
some basic rules are followed (e.g. never passing "raw" pointers of
instances manged by shared pointers). The safer
std::enable_shared_from_this<> approach continues to be supported.

This modification taps into some newer C++14 features (if present) to
generate function signatures considerably more efficiently at compile
time rather than at run time.

With this change, pybind11 binaries are now *2.1 times* smaller compared
to the Boost.Python baseline in the benchmark. Compilation times get a
nice improvement as well.

Visual Studio 2015 unfortunately doesn't implement 'constexpr' well
enough yet to support this change and uses a runtime fallback.