Colorize the weblist output

[rakyll]

It is sometimes hard to read the weblist output because of the volume of data presented on the pages. Colorizing the expensive lines with shades of red to yellow would help the users to point out the expensive sections easily.

For each function call, we can look at the distribution of the cost. The 80th percentile can be red, 60th can be yellow, etc.

An example output is below:

[rakyll]

/cc @aalexand

[aalexand]

Agree, this is useful.