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

bcc: add lru_hash and lru_percpu_hash map types