v0.4 — New flags, help, new tcell

• 9ddc78b upgrade version to 0.4
• b20471c deps: upgrade tcell (#45)
• 94ad570 add --noinput flag (#50, #33)
• 3e81993 add usage info with --help flag (#35)
• 8aa1f8f add --buf flag for specifying buffer size
• 3a63622 add -c flag for initial pipeline command (#11)
• 5dc341c add -e multi-flag for custom shell

New flags:

      --buf megabytes          input buffer size & pipeline buffer sizes in megabytes (MiB) (default 40)
  -e, --exec command           command to run pipeline with; repeat multiple times to pass multi-word command; defaults to '-e=$SHELL -e=-c'
      --noinput                start with empty buffer regardless if any input was provided
  -c, --pipeline commands      initial commands to use as pipeline (default empty)