[RFC PATCH v5] Input/Output Terminal Abstraction

This expands on Marcel Holtman's 2023-12-22 RFCv4 patch for an
input/output terminal abstraction.

Substantive changes from the v4 version:

  * Return status is 'int' rather than 'bool' with 0 as success and <
    0 as failure where the failures are negated POSIX error
    numbers. This removes the need for system integrators to intuit
    their own errors on a previously-false Boolean return status.

  * Makes 'l_term_set_{input,output}' public functions.

  * Adds observer functions for the terminal rows and columns.

  * Adds a modifier function for the terminal bounds.

  * Adds:

      - l_term_io_func_t
      - l_term_set_io_handler
      - l_term_process
      - l_term_io_callback

    Collectively, these make the abstraction run loop adaptable with a
    default callback that can be easily used with ELL's run loop,
    'l_term_io_callback'.

  * Adds 'l_term_[v]print' which complete the output interface.

    Of course, its always possible to perform this outside of an atop
    the existing functions; however, this eliminates integrators from
    having to manage the buffers necessary to do this.

This has proven to work well with the RFCv4 l_edit interfaces and the
corresponding demo-{cli,edit} applications.

Grant Erickson (4):
  term: Initial revision.
  ell: Add include directive for 'ell/term.h'.
  ell/Makefile: Added 'term.[ch]' to HEADERS and SOURCES.
  term: Added 'l_term_*' symbols.

 Makefile.am |   2 +
 ell/ell.h   |   1 +
 ell/ell.sym |  21 +++
 ell/term.c  | 487 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 ell/term.h  |  69 ++++++++
 5 files changed, 580 insertions(+)
 create mode 100644 ell/term.c
 create mode 100644 ell/term.h

-- 
2.42.0