Add geiser-eval-buffer & geiser-eval-buffer-and-go

Hello,

This commit adds two functions, `geiser-eval-buffer` and `geiser-eval-buffer-and-go`.  It also includes adding matching keybindings that coincide with the current keyboard binding theme (i.e., `C-c C-b` and `C-c M-b`, respectively).  I have included updates to the documentation as well.  Please let me know if there is any interest in this, or if any changes need to be made.  Thanks!

Nick Parker