line_buffer API
===============

The line_buffer library provides a convenient interface for
mostly-line-oriented input.

Each line is not permitted to exceed 10000 bytes.  The provided
functions are not thread-safe or async-signal-safe, and like
`fgets()`, they generally do not function correctly if interrupted
by a signal without SA_RESTART set.

Calling sequence
----------------

The calling program:

 - specifies a file to read with `buffer_init`
 - processes input with `buffer_read_line`, `buffer_read_string`,
   `buffer_skip_bytes`, and `buffer_copy_bytes`
 - closes the file with `buffer_deinit`, perhaps to start over and
   read another file.

Before exiting, the caller can use `buffer_reset` to deallocate
resources for the benefit of profiling tools.

Functions
---------

`buffer_init`::
	Open the named file for input.  If filename is NULL,
	start reading from stdin.  On failure, returns -1 (with
	errno indicating the nature of the failure).

`buffer_deinit`::
	Stop reading from the current file (closing it unless
	it was stdin).  Returns nonzero if `fclose` fails or
	the error indicator was set.

`buffer_read_line`::
	Read a line and strip off the trailing newline.
	On failure or end of file, returns NULL.

`buffer_read_string`::
	Read `len` characters of input or up to the end of the
	file, whichever comes first.  Returns NULL on error.
	Returns whatever characters were read (possibly "")
	for end of file.

`buffer_copy_bytes`::
	Read `len` bytes of input and dump them to the standard output
	stream.  Returns early for error or end of file.

`buffer_skip_bytes`::
	Discards `len` bytes from the input stream (stopping early
	if necessary because of an error or eof).

`buffer_reset`::
	Deallocates non-static buffers.