mavlink & system: add events interface

- sending protocol
- uorb event message & template methods for argument packing
- libevents submodule to send common events and handle json files
- cmake maintains a list of all (PX4) source files for the current build
  (PX4 modules + libs), which is used to extract event metadata and
  generate a json file

Tools/astyle/files_to_check_code_style.sh

@@ -16,6 +16,7 @@ exec find boards msg src platforms test \
     -path src/drivers/uavcannode_gps_demo/libcanard -prune -o \
     -path src/drivers/uavcan/uavcan_drivers/kinetis/driver/include/uavcan_kinetis -prune -o \
     -path src/lib/ecl -prune -o \
+    -path src/lib/events/libevents -prune -o \
     -path src/lib/matrix -prune -o \
     -path src/lib/parameters/uthash -prune -o \
     -path src/modules/gyro_fft/CMSIS_5 -prune -o \

Tools/compress.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+import argparse
+import lzma
+
+parser = argparse.ArgumentParser(description="""Compress a file with xz""")
+parser.add_argument('filename', metavar='file', help='Input file (output: file.xz)')
+
+args = parser.parse_args()
+filename = args.filename
+
+def save_compressed(filename):
+    #create xz compressed version
+    xz_filename=filename+'.xz'
+    with lzma.open(xz_filename, 'wt', preset=9) as f:
+        with open(filename, 'r') as content_file:
+            f.write(content_file.read())
+
+save_compressed(filename)
+