phi-search-limit improvements

[wavexx]

Somehow the handling of phi-search-limit is sub-par.

I often use incremental search to move the cursor (I find the behavior much more intuitive than ace-cursor or move-to-char), but if I search for a single space I reach the phi-search-limit immediately.

I think that phi-search-limit should be handled differently: if the limit is hit, just stop highlighting/counting (that is, create overlays for the first phi-search-limit matches and show 1/NaN in the search count or something similar), but still start the search.

This would allow to search for common strings in any circumstance, without really affecting performance.

[zk-phi]

I don't have time to implement now, but I also think it's a necessary feature (#45).

(contributions are welcome!)