add modes to conv function

[jasonsychau]

add modes to conv function

[galenlynch]

This is a very big change to how conv works with no explanation. Besides changing convolution from frequency domain to time domain, and thereby changing its algorithmic complexity, this commit would also make conv no longer work with arbitrary dimensions (and instead only work with vectors), as well as no longer accepting inputs with arbitrary indexing (and instead only work with arrays that start at index one).

Supporting something like Matlab's convolution modes could be done just by cropping the output of conv. If you want to support these modes at the library level, then that seems like a better place to start.

[galenlynch]

If you want to add this functionality, please implement it in a way that preserves the existing functionality and performance.

[jasonsychau]

Sure, I’ll review at later time.

Thanks, Jason