Fix few non-"const" casts that are no longer necessary

Xorg API changed and we can now remove all the useless non-"const" casts
that were needed before.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
build: AM_CONFIG_HEADER -> AC_CONFIG_HEADER

AM_CONFIG_HEADER is no longer supported in newer autotools releases. Fix
this and use AC_CONFIG_HEADER instead.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Bump version to 0.3

This release includes some build fixes that are necessary to get this
driver working with newer Xorg releases.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>