New architecture

[jpikl]

Instead of a single executable rew with all of the filtering functionality, let's split the project into more smaller cli tools, where every tool does one separate thing.

• Previous filters will be implemented as separate rew subcommands. For example:
  • t filter becomes rew trim [-s|--start] [-e|--end] subcommand.
  • r filter becomes rew replace <what> [replacement] subcommand.
  • c filter becomes rew seq subcommand.
  • C filter becomes rew parent | rew count where parent subcommand prints parent directory and count subcommand print number of occurrences of input lines.
• Pipeline composition will be done using rew x subcommand:
  • Former usage: rew 'img_{C}.{e|l|r:e}'
  • New usage: rew 'img_{seq}.{ext | lower | replace e}'
• rew will run {a | b | ...c} pipelines in separate threads
• Every pipeline will consume/produce lines.
• Every subcommand will support -0, --null flag to process NUL separated lines.
• There will be REW_NULL environment variable to enable -0, --null behavior globally.
• Former cli options for custom input/output line separator will be implemented as a separate subcommands split and join.
• Alternative output modes (diff/json lines) will not be supported anymore.
• Auxiliary mvb/cpb tools will be dropped in favor of generation of executable shell code.