Bulker

- Fixed a bug that prevented use when installed in non-writable directory
- Added ability to use bash autocompletion

- Update to yacman 0.8.0, fixing references to internal config attributes.
- Add documentation and clarity for the `shell_prompt` option
- Fixed bug with relative crate root folders

- Fixed bug in bulker reload.

- EXPERIMENTAL: Added `bulker cwl2man` to create a bulker manifest from a CWL file.
- BREAKING CHANGE: Renamed the `bulker load` arguments: the `--manifest` short arg changed from `-f` to `-m`; `--force` changed from `-r` to `-f`. This is to be more consistent with the names. Since I doubt many people are using this in script, I don't think this will break much, if anything.
- Added new option for `-r`, `--recurse` to `bulker load`, which recursively re-loads all imported manifests.
- Added new `bulker reload` command, that reloads all manifests.
- Added `bulker envvars`, which allows you to list, add (`-a VAR`), or remove (`-r VAR`) environment variables to the bulker config from the CLI.
- Added `bulker unload` to remove a loaded manifest.

- Allowed `bulker run` to gracefully handle interrupts, passing them to the child process.
- Implemented `-p`, which doesn't update prompts, for compatibility with jupyter notebooks
- Fixed a bug with using the default config
- Added capability to exclude volumes from specific containers
- Fixed a bug with singularity exec template
- Dropped support for Python 2

- Added bulker shell prompts for both normal and strict modes
- Added custom shell prompts (experimental!)
- Added `bulker inspect`
- Added env variables $BULKERCRATE, BULKERPROMPT, and BULKERSHELL.
- Changed the behavior of normal mode to set bulker path *after* calling the rcfile.
- Changed built-in singularity template to accommodate singularity version 3
- Changed method for accommodating zshell.
- Removed support for python 3.4