Add width qualifier to uniform init

Similar to "sigma" for the gaussian initializer, this
allows to run the chain in a specific range but initialize
it in a smaller range.

src/fitting/ensemble-samplers/emcee.sl

@@ -998,7 +998,7 @@ private define emceeInitUniformPick (init, engine) %{{{
   k = 0;
   _for i (0, length(c)-1) {
     _for j (0, c[i]-1)
-      engine.walkers[j+k] = _max(p[i].min, _min(p[i].max, rand_uniform(numParameter)*(p[i].max-p[i].min)+p[i].min));
+      engine.walkers[j+k] = _max(p[i].min, _min(p[i].max, rand_uniform(numParameter)*init.width*(p[i].max-p[i].min)+p[i].min));
     k += c[i];
   }
 }
@@ -1006,8 +1006,9 @@ private define emceeInitUniformPick (init, engine) %{{{
 %}}}
 private define emceeInitUniform () %{{{
 {
-  variable init = struct { @EmceeInit };
+  variable init = struct { @EmceeInit, width };
   init.pick = &emceeInitUniformPick;
+  init.width = _min(_max(qualifier("width", 1.0), 1e-3), 1.0);
 
   return init;
 }