When the target process is missing the required USDT probes, it can
be a simple mistake (e.g. attaching a script as Java to a Python
process), or a runtime that is not instrumented with the required
probes. Attempt to gracefully handle the error and print a helpful
message instructing the user why the error might have occurred.

```
$ uthreads -l java $(pidof python)
Error attaching USDT probes: the specified pid might not contain
the given language's runtime, or the runtime was not built with the
required USDT probes. Look for a configure flag similar to
--with-dtrace or --enable-dtrace. To check which probes are present
in the process, use the tplist tool.
```

Filter out collections that are shorter than x milliseconds by using
`ugc -M x`. Display only collections that contain a certain string s
in their description by using `ugc -F s`. The latter option is not
implemented in the kernel, but rather just before printing the event
in the user script (for simplicity), and documented as such.

Add Node support for gc__start and gc__done probes, which
includes GC type flag parsing.

For runtimes that make it available, we now extract GC
event information such as heap sizes and print this
information in addition to the GC duration and timestamp.

`ugc` monitors GC start and end events in Java, Python,
and Ruby, printing out a message when a GC cycle completes
along with the duration of the GC and an optional
additional description that depends on the target language.

NOTE: This WIP does not have any interesting additional
descriptions yet.

Usage example:

```
ugc java 1448	# monitor Java GCs in process 1448
```