FastPedestal + optimizations in the cluster finder (#341)

Optimized pedestal tracking with FastPedestal and performance improvements to the cluster finder. 
- ~2x faster hitting 14k FPS on benchmark dataset on 16 core threadripper pro


**Changes**
- No bounds check on interior of frame. (only within half of a cluster)
(~15% improvement)
- Cache threshold (std*n_rms) Biggest improvement comes from not
computing std for each access
- Cache pedestal subtracted frame
- Switched to FastPedestal which assumes we reached steady state

**Things tried but rejected:**
- Always store cluster values, commit on val==max (~15% drop in frame
rate)

**Options**
- using 16 bit clusters and 16 bit pedestal. (slows down the single
threaded case but allow us to reach 12k with multi threading)

**Other notes on performance**
- Passing in memory frames from python and doing nothing: 0.8us/frame
- Passing + pedestal subtraction: 28us/frame
- Passing + pedestal + cluster finding (no store): 652us/frame
- Passing + pedestal + cluster finding: 886 us/frame

python/src/bind_ClusterVector.hpp

@@ -15,7 +15,6 @@
 #include <pybind11/stl_bind.h>
 
 namespace py = pybind11;
-using pd_type = double;
 
 using namespace aare;