Whitespace changes to match Gnome style
Use G_ADD_PRIVATE to add context private data
Make our VAPI name gsound, not gsound-1.0

We don't add a version number to anything else apart from the
GI giles (though perhaps we should...), and in any case VAPI
file names generally follow pkgconfig names
Make GSoundContext a sealed/final class

GSoundContext has no virtual methods, nor even any properties --
there really is nothing useful that can be acheived be subclassing
it, so we may we well forbid it. It can always be "unsealed"
later if necessary.
Use g_clear_pointer consistently

Kind of pointless, but there we go
Whitespace changes for Gnome/GTK header style
Add the start of some documentation
Rename gsound.[ch] to gsound-context.[ch]

Filenames should be the same as class names, I think.

Also, add a new gsound.h header which does nothing but include
gsound-context.h, and take this opportunity to do a little
tidying of Makefile.am
Move attributes to their own header, mainly for docs purposes
Tinker with documentation
Add docs master template, still need to fill in details
Document more functions