Aperf: Allow to use custom PMU

Allow the user to specify a custom PMU file to be used during aperf
record. This custom PMU file must be in the expected format.

To aid in the creation of the custom PMU file, add a sub-command.

'aperf custom-pmu' - an interactive sub-command to create custom PMU.
This allows the user to create a file from scratch or modify an existing
PMU config aperf already knows about. The custom file generated can be
used by specifying '--pmu-config' with 'aperf record'.

Additionally, a pmu-config file can be verified by specifying --verify
along with --pmu-file with 'aperf custom-pmu'.

Create a tmp directory for record and report

Also, move to using references where possible for the Data trait.

Add support for catching signals

This is used if the user ends an Aperf run using Ctrl+c or kill <pid>.
We send the same signal to any child processes launched by aperf.

Added java virtual machine profiling and flamegraph generation

Wait for 'perf record' to finish

Fix compiler warning

Remove unnecessary .clone().

Update README.md

Flush buffer after forming archive

Data remains in the GzEncoder. Ensure it is flushed before performing
any other operations on the tarball.

This fixes a bug in the report generation, where the tarball of the raw
data is copied to data/archive/. When trying to untar the file, the data
is corrupted and unuseable.

Allow specifying non-PWD for aperf record/report

An aperf_tmp is used for all intermediate steps aperf performs when
forming the report.

Visualizer updates

Updates:
* CPU Utilization graph y-axis is always 100%.
* Diskstat read, sector graph updates.
* VMStat graph updates.