uflow: Trace method execution flow

uflow: Trace method execution flow

This tool traces method executions and prints out messages
with a nesting depth indicator that allows relatively easy
visualization of program flow. To reduce overhead, `-C` and
`-M` switches take class and method prefixes to filter the
output by. The filtering takes place in the BPF program, so
the unnecessary data never ends up in user space.

Usage examples:

```
uflow java 185
uflow -M index python 180
uflow -C 'IRB::Irb' ruby 10041
```