Sergey Lyskov pointed out that the trampoline mechanism used to override
virtual methods from within Python caused unnecessary overheads when
instantiating the original (i.e. non-extended) class.

This commit removes this inefficiency, but some syntax changes were
needed to achieve this. Projects using this features will need to make a
few changes:

In particular, the example below shows the old syntax to instantiate a
class with a trampoline:

class_<TrampolineClass>("MyClass")
    .alias<MyClass>()
    ....

This is what should be used now:

class_<MyClass, std::unique_ptr<MyClass, TrampolineClass>("MyClass")
    ....

Importantly, the trampoline class is now specified as the *third*
argument to the class_ template, and the alias<..>() call is gone. The
second argument with the unique pointer is simply the default holder
type used by pybind11.

pybind11::args should have been derived from tuple

args was derived from list, but cpp_function::dispatcher sends a tuple to it->impl (line #346 and #392 in pybind11.h).  As a result args::size() and args::operator[] don't work at all.  On my mac args::size() returns -1.  Making args a subclass of tuple fixes it.

Increase available information on invocation error.

Cache C/C++ compilation

Fixed typo in NumPy example which prevented compilation

Refactoring bind_vector to take std::string

Refactoring bind_vector to take std::string to avoid capture of potentially temporary char const * when calling vector_if_insertion_operator

Fixing VC build, apparently MSVC implementation of std::is_default_constructible had no bool() operator

Adding documentation for value_error. Fixing various formatting issues. Removing redundant binding for C++ style methods. Adding bindings for iterator and slicing protocol. Extending examples.

Adding Python-style modifiers for vector. Wrapping has_insertion_operator_implementation in _MSC_VER ifdef’s. Adding ‘!=0’ instead of bool cast’s.

add extra constructors in numpy.h