PushConstant class

A utility to provide data to shader through push constant.

The PushConstant type exposes the following members:

Constructor	Description
`__init__(self)`	Constructor of the `PushConstant`

Method	Description
`write(self, mat)`	Write the matrix to the constant
`write(self, n)`	Write a int value to the constant
`write(self, f)`	Write a float value to the constant
`write(self, vec)`	Write a 4-component vector to the constant
`write(self, vec)`	Write a 3-component vector to the constant
`write(self, x, y, z, w)`	Write a 4-component vector to the constant
`commit(self, stage, command_list)`	Commit prepared data to graphics pipeline.