upgrade luarocks

ref #822
Remove version{4,5,6,7}.txt
Update CONTRIBUTING.md and README.md #740

- recommend task/subtask convention for commit messages
Merge pull request #1116 from fornwall/remove-versions-txt

Remove version{4,5,6,7}.txt
Merge pull request #1088 from justinmk/upgradeluarocks

upgrade luarocks
test: Remove cleanup function definition from run-api-tests.exp

This function is now injected automatically when running the python-client tests
wstream: Implement wstream_set_file

It's analogous to rstream_set_file but only supports pipes(Support for regular
files may be added later). This function was added to support creating API
channels via stdout.
channel: Fix channel not being closed when the RStream reaches EOF
channel: fix channel buffer size
channel: Implement channel_from_stdio function

This function can be used to create an API channel that reads/writes from/to
stdin/stdout
api: Implement '--embedded-mode' command-line option

This option makes nvim run in "embedded mode", which creates an API channel via
stdin/stdout and disables all terminal-related code
test: Run tests in embedded mode on travis
Merge PR #1060 'Implement --embedded-mode command-line option'
clang: Null pointer passed as an argument to a 'nonnull' parameter #1090
Add 'bit' to the list of lua dependencies

- ex_cmds.lua requires the 'bit' module
Merge #1123 "Add 'bit' to the list of lua dependencies"
Update luarocks: Use commit with correct version number.
Merge pull request #1124 from fwalch/luarocks-version-number

Update luarocks: Use commit with correct version number.
msgpack-rpc: Accept method names in requests
msgpack-rpc: Always use arrays when sending events or calls

This is required by the msgpack-RPC specification. Also, the
send_call/send_event functions were refactored to accept a variable number of
arguments