Reverse delay

[jswill88]

Issue #1365

Adds a reverse delay effect using the DelayLine worklet. It works by creating a delay line that is twice as long as the delay time and then reading the "mirror" index of the write node so the previously written nodes are read in reverse order. For example. if the delay line was length 10, this is what would be read at each write index:

write index	read index
5	4
6	3
7	2
8	1
9	0

I used this as a reference: https://ccrma.stanford.edu/~jingjiez/portfolio/echoing-harmonics/pdfs/A%20Pitch%20Shifting%20Reverse%20Echo%20Audio%20Effect.pdf

There is an example page at examples/reverseDelay.html

Let me know if you have any questions or if there is anything I can improve.