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
```

`ucalls` is a new tool that uses the USDT probes in high-
level languages (Java, Python, Ruby) to summarize the
number of method calls and optionally their latency. This
is similar to `funccount` and `funclatency` but for methods
in Java, Python, Ruby, and other languages that might have
USDT probes for method entry and exit.

`ucalls` uses the `method__entry` and `method__return`
probes in Java and Ruby, and the `function__entry` and
`function__return` probes in Python. The Python probes are
not as accurate because they do not report the class name,
but are still useful.

The optional `-L` switch indicates whether latency numbers
are required. By default, only the number of calls to each
method is printed. The `-T` switch filters out the top
methods (by number of calls or total latency).

Add USDT support to C++ API

Improve linear histogram limit, and improve error message.

runqlen: use bpf_get_smp_processor_id()

add runqlen tool

check effective userid on run #850

add Quick Start Guide for bcc docker

docs: Update eBPF features list

Update of BPF features list, following the release of kernel 4.9.

offwaketime: update with get_stackid fixes #437

Expose perf event support in C++ API

Improve C++ API perf buffer polling

add support for bpf map flags

Make sure program FDs get cleaned up correctly

Fix for issue 829 I reported 

Needed to make array initialized to null before bpf_probe_read as the
verifier was rejecting the original code. will probably need to fix the
tutorial as well

updating my local repo

Fix bug of missing to install simple_tc.py

Signed-off-by: Zhiyi Sun <zhiyisun@gmail.com>

examples/networking/CMakeLists.txt set $EXAMPLE_PROGRAMS twice. The
second one(tc_perf_event.py) overwirte the first one(simple_tc.py).
Signed-off-by: Zhiyi Sun <zhiyisun@gmail.com>

Add support for aarch64

ABI for aarch64: register x0-x7 are used for parameter and result. In
bcc, there are 6 parameter registers are defined. So use x0-x5 as
parameter. frame pointer, link register, stack pointer and pc are added
in PT_REGS_xx according to arm64 architecture.

syscall number of bpf for aarch64 are defined in Kernel
header uapi/asm-generic/unistd.h.
Signed-off-by: Zhiyi Sun <zhiyisun@gmail.com>

Avoid unexpected log message on BPF program load error