Add a workaround for KDevelop not recognizing 'restrict'
Use a simpler U64 macro to make 64-bit constants
Rename Filter param member to LpFilter
Don't store the effect slot in SendParams

This makes it much more like DirectParams.
Use a macro for the silence threshold
Start using a simpler method for error handling

This helps avoid the al_try/al_throwerr/al_endtry stuff.