Accelerate `rlx_prv_discover` provider

Introduce option `enable_shallow_app_discovery` which is disabled by
default.

When enabled searching for `*.app` files is done by using
`filelib:wildcard/1` and doesn't recursively traverse all directories
under `libs_dir` root dirs.

Instead its assumed that each directory on `libs_dir` list contains a
flat list of application dirs or is an app itself.
Added a command line override for the sys_config setting.
use vm.args in basic bin script
Merge pull request #137 from tsloughter/vm_args

use vm.args in basic bin script
Merge pull request #133 from mattrudder/sys_config_cmdargs

Added a command line override for the sys_config setting.
Merge pull request #101 from konradkaplita/accelerate_discover_provider

Accelerate application discovery
Added note about rebar version
Merge pull request #145 from jwilberding/readme

Added note about rebar version
Replace relcool with relx in example config.
Merge pull request #150 from rlipscombe/rl-relcool-to-relx

Replace relcool with relx in example config.
Allow overriding RUNNER_LOG_DIR
Merge pull request #152 from rlipscombe/rl-runner-log

Allow overriding RUNNER_LOG_DIR
Update startup script to allow overriding config location.
Ignore rebar if it needed to be downloaded.
Merge pull request #155 from rlipscombe/rl-override-config

Allow VMARGS_PATH and CONFIG_PATH to be overridden
Give release scripts ability to handle directories with spaces
Merge pull request #154 from nuex/quote_vars

Give release scripts ability to handle directories with spaces
Windows support
Windows build instructions
Merge pull request #159 from nuex/windows

Windows Support