Runcommands

Added

- Default args for the main script will now be read from `runcommands.cfg` or
`setup.cfg` if one of those is present and contains a `[runcommands]`
section.
- Added ability to list available envs to main script (`--list-envs`).
- Added support for bool-or-type options. This is used with `hide` options.
- Added support for args that specify choices. Added `choices` arg to
`Command`.
- Added support for `Enum` args. These args will be limited to the choices
specified by the enum.
- `commands_module` is now included in config.

Changed/Improved

- Command line option names for `dict` and `list` args are now made singular
when they end with an `s`. From the command line, dicts and lists are created
by using a given option multiple times. Using a singular name makes this more
clear.
- Improved `show-config` command. Added `--flat` flag (don't nest config).
Added `--values` flag (show values only without keys. Added ability to
specify multiple items. Added `--exclude` option.
- Made default type of `hide` args for all commands `bool_or(Hide)`.
- Improved handling of arg types in general.
- Removed fill/wrap code; use `textwrap.fill()` from the stdlib instead.
- Wrapped entire body of main script in try block. `RunCommandsError` is now
raised in some places. These keep the main script from blowing up with
a stack trace in cases where it's better to abort with a nice error message.

Fixed

- Fixed a one-off bug with `--` in the main script. Skip over it so it's not
treated as a command arg.
- Fixed an issue in `Printer.print()` where the `file` arg wasn't being passed
down to `print()`, which was causing warning, error, and debug messages to be
sent to stdout instead of stderr.
- Fixed `RawConfig` so it doesn't read files when adding items or cloning.

- Improved command env handling and options.

- Fixed a bug when raising `TimeoutExpired` exception in `LocalRunner`. The
captured output data is bytes and needs to be decoded.
- Improved handling of non-existent commands module or config file. Catch
exceptions and raise an appropriate `RunCommandsError` instead. The main
script catches these errors and aborts with a useful message instead of
spewing a traceback.
- Improved `release` command's automatic next version detection. In particular,
it can now derive `1.0aN` from `1.0aM`.

- Fixed potential decoding errors when capturing subprocess data. Captured data
is no longer decoded eagerly, which avoids decoding errors when the data read
ends with an incomplete Unicode byte sequence. This was an issue for commands
that output a lot of data, like `npm install`.

- Improved input/output mirroring/capture in `LocalRunner`.
- Fixed input mirroring issue with subprocesses that accept single character
input (like `less`).
- Added loop to read until no more data is available after subprocess exits.
- Added `COLUMNS` and `LINES` to subprocess environment when using PTY so
output isn't constrained to the default terminal size.
- Made more robust by checking for closed streams when reading, closing PTY
file descriptors, etc.
- Moved read/mirror/capture code into its own module for potential reuse.
- Made an attempt to fix the Paramiko remote runner strategy using the
`select`-based reader, but it didn't work because the file handles returned
by `SSHClient.exec_command()` aren't "real" files (they don't have
a `fileno()` method).

- Simplified handling of input/output in `LocalRunner`. Instead of firing up
reader threads, this version uses `select`. This seems to actually work in
all cases now (PTY vs non-PTY), but it won't work on Windows. It also breaks
the Paramiko remote runner strategy (since `NonBlockingStreamReader` was
removed). It might be possible to create a thread-based version of the same
logic...
- In `get_default_prepend_path`, bad asset paths are now skipped over and
a warning is printed. This fits with how non-existent path directories are
skipped. Previously, a bad asset path would cause a nasty `ImportError`.
- Improved `util.asset_path`:
- Inject `config` into path at top instead of at bottom.
- Raise a better error when a path contains an unimportable package.
- Added `clean` command.