added 'hide_x_bottom_lines' and 'sort_alphabetically' options

[BrVer]

Tool works nice, however I missed some functionality:

1. ability to not display X bottom lines of the stacktrace, as it's usually some rails initialization stuff which only takes extra place
2. ability to sort stacktraces alphabetically, so the same stacktraces will be grouped into one big column instead of being splitted across the chart

The second option gives next benefits:

• it's really easy to visually determine which parts of code take the most CPU time
• chart size is reduced dramatically, especially if you're using much loops in your code (for me it reduced from 40MB, which crashed browser tab, to ~1.5MB which can be opened without such risk)
• original flamegraph (https://github.com/brendangregg/FlameGraph) works this way, so it will be convenient to add such option