Add documentation for clamp_max() and clamp_min()
Add documentation for clamp_max() and clamp_min()

This closes #267

du2016/prometheus-docs,Cepave/openfalcon.io,pdbogen/docs,vic3lord/docs,chosenken/docs,vic3lord/docs,ddfreyne/prometheus-docs,prometheus/docs,tcolgate/docs,du2016/prometheus-docs,pdbogen/docs,pdbogen/docs,ddfreyne/prometheus-docs,chosenken/docs,open-falcon/open-falcon.github.io,chosenken/docs,prometheus/docs,Cepave/openfalcon.io,vic3lord/docs,tcolgate/docs,tcolgate/docs,Cepave/openfalcon.io,du2016/prometheus-docs,ddfreyne/prometheus-docs,prometheus/docs,chosenken/docs,ddfreyne/prometheus-docs,open-falcon/open-falcon.github.io,open-falcon/open-falcon.github.io