Merge remote-tracking branch 'origin/master' into 1.6

doc/sphinx/book/box/box_index.rst

doc/sphinx/book/box/box_space.rst

doc/sphinx/book/box/index.rst

doc/sphinx/book/box/limitations.rst

doc/sphinx/book/configuration/cfg-basic.rst

doc/sphinx/dev_guide/building_from_source.rst

src/box/box.cc

src/box/error.cc

src/box/error.h

src/box/index.cc

src/box/iproto.cc

src/box/lua/stat.cc

src/cbus.cc

src/cbus.h

src/rmean.h

test/box/misc.result

test/box/stat.result

test/box/stat.test.lua

test/box/stat_net.result

test/box/stat_net.test.lua