Don't export function symbols outside the package.

glowDebugCallback still need to be fixed.
Merge pull request #13 from capnm/patch-1

Don't export function symbols outside the package.
Add XML spec and doc files to the repository.

Fixes #14.
Add a README explaining why the xml dir exists.
Switch p/P function pointer prefixes to gp/GP to avoid Windows conflicts.
Add package-unique suffixes to debug functions.
Update prebuilt packages to allow multiple glow packages in the same program.

Fixes #12.
Format package.go.
Add an "all" pseudo-profile for generating all-version packages.

For community consideration in Issue #15.
Add an "all" pseudo-version for generating all-version pacakges.

For community consideration in Issue #15.
Update the Makefile to match the current prebuilt packages.
Add lenientInit flag to allow missing functions at Init time.

Generalizing support for Issue #15.
Add documentation for the new version=all and lenientInit flags.
Add a format target to the Makefile.
Update glow to use the go-gl import path.
Remove the broken boolean indicators for functiona and extension availability.

Update the generated packages to reflect the removal. As a side effect
update the packages to the new go-gl path, and go fmt the contents.
Update the README to reference go-gl.
Add dropped build-fixing changes.