lisa.trace: Add text trace parser

BREAKING CHANGE

Parse text traces based on the output of `trace-cmd report -R`
Also add some convenience parser for the human readable format.

Quick & dirty events based on calling trace_printk() in the kernel now
need to be prefixed with "trace_printk@" when parsed in lisa:

 kernel: trace_printk("foo: field1=42 field2=hello world")
 lisa  : trace.df_events('trace_printk@foo')

Matching on calling function name can be achieved with:

 kernel: (called from function foo()) trace_printk("field1=42 field2=hello world")
 lisa  : trace.df_events('trace_printk@func@foo')

Similarly, events generated from userspace by writing to
/sys/kernel/debug/tracing/trace_marker need to be prefixed:

 user: echo "foo: field1=42 field2=hello world" > /sys/kernel/debug/tracing/trace_marker
 lisa: trace.df_events('userspace@foo')

Note: The format is expected to follow the raw format of
`trace-cmd report -R`, such as in the example.

Also, event field names are now reflecting the name they have in the
kernel. Since trappy has non-optional renaming of the fields, client
code update might be needed. The recommended way is to use the high
level df_* functions from the analysis where applicable, since they will
give friendlier names and can usually cope with multiple formats of the
event across kernel versions if necessary.