Display the percent of the total request any symbol took.
Put percent of total in same cell as function.

Having them in the same row/cells makes reading the results a bit
easier, as the rows highlight at the same time.
Show percent of request for parent function as well.

It can be useful for finding functions that have a high self cost.
Update tests for nbsp.
Merge pull request #103 from perftools/symbol-percentage

Display function percentage of total in symbol view