Add API calls to reserve channels and play instrument

In applications such as games we may want to trigger certain samples
interactively. Add calls to reserve a number of channels, and to play
arbitray instruments in any channel.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix buildsystem dependency generation

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Add API calls for foreign sample playing

Allow us to inject foreign samples into our playing mod. This can be
used in applications such as games to play sound effects.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix instrument event injection

Allow injecting events in reserved channels for game sound effects.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Add API call to create empty module

We may want to have the player running to play sound effects but without
any background music. Instead of loading an empty module, we can just create
a dummy one.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>