Getter of bitmap Buffer

Hello,

I'm student in engeneering school and I Have to implement some new function in your module. I add three new function to use bitmap buffer in numpy for example.
These three functions are
Bitmap.get_bpp (To get the number of bits per pixel of screen)
Bitmap.get_buffer_length ( To get the length of the buffer)
Bitmap.get_buffer(To get the...buffer)
So I hope you'll accept my pull request
Thank you and have nice day