Std unit conversions (#259)

* Added conversion constants

* implemented std unit conversion

* changed centerToFront ratio

Changed weight distribution ratios used to calc center of gravity distances to align closer to manufacturer specs

* implemented std unit conversion

* remove unused conversion

* reverted wheelbase conversion

slight change to pilot wheelbase

* removed redundant conversion

* removed incorrect/unused conversion

* removed class that now exists in honda/values.py

* redirect Cruisebuttons call

* redirect Cruisebuttons call

* Update interface.py

* Update numpy_fast.py

Refactor

* Update numpy_fast.py

* Update numpy_fast.py

-encapsulated get_interp 
-reduced calls to len() for iterable input

common/numpy_fast.py

@@ -1,29 +1,18 @@
 def int_rnd(x):
   return int(round(x))
 
-
 def clip(x, lo, hi):
   return max(lo, min(hi, x))
 
-
 def interp(x, xp, fp):
   N = len(xp)
-  if not hasattr(x, '__iter__'):
+  def get_interp(xv):
     hi = 0
-    while hi < N and x > xp[hi]:
+    while hi < N and xv > xp[hi]:
       hi += 1
     low = hi - 1
-    return fp[-1] if hi == N and x > xp[low] else (
-      fp[0] if hi == 0 else
-      (x - xp[low]) * (fp[hi] - fp[low]) / (xp[hi] - xp[low]) + fp[low])
-
-  result = []
-  for v in x:
-    hi = 0
-    while hi < N and v > xp[hi]:
-      hi += 1
-    low = hi - 1
-    result.append(fp[-1] if hi == N and v > xp[low] else (fp[
-      0] if hi == 0 else (v - xp[low]) * (fp[hi] - fp[low]) / (xp[hi] - xp[low]
-                                                               ) + fp[low]))
-  return result
+    return fp[-1] if hi == N and xv > xp[low] else (
+      fp[0] if hi == 0 else 
+      (xv - xp[low]) * (fp[hi] - fp[low]) / (xp[hi] - xp[low]) + fp[low])
+  return [get_interp(v) for v in x] if hasattr(
+    x, '__iter__') else get_interp(x)