Ensure numbers remain as numbers.

[crabmusket]

Previously, the call to toFixed would turn numbers into strings, which was playing havoc with models bound to <input type="number"> elements.

[crabmusket]

Just realised this is an incorrect solution! I'll rebase the commit, but I'm actually stumped as to what solution you'd prefer. The problem is the toFixed call in roundStep. It results in a string, which is bad. However, it also allows the values bound to the bubbles (in, e.g., "translate({value: #{refLow}})") to have a fixed precision, which is good. I think the correct solution is to perform the rounding just before translation.

[crabmusket]

I've ended up rewriting the default translation function:

scope.translate = (value) -> value.value?.toString()

This means that a provided translate function is responsible for ensuring it returns a string. This doesn't handle rounding, but I think that could be accomplished in this way, instead of calling toString.