faster splitter

[Jack Stouffer via Digitalmars-d]

On Monday, 23 May 2016 at 13:20:55 UTC, Andrei Alexandrescu wrote:
> Most uses are forward, so perhaps it's best to eliminate the 
> bidirectional bookkeeping if it adds overhead, and confine 
> those to a separate function e.g. splitterBidirectional. There 
> is precedent for that in Phobos. -- Andrei

I don't see the value add that things like filterBidirectional 
give when the back and popBack functions can be static if-ed in 
or out the normal filter. filterBidirectional always felt like a 
relic of a time when static if's didn't exist, even though I know 
that's not the case.