calc 2.12.6.7 release

The following are the changes in this release:

Fixed errors in various help files such as:

    mat randbit seed srandom types

Removed the MAXSTRING symbol because it was no longer used by calc.

Increased HIST_SIZE (depth of the history stack) from 10k to 32k.

Increased TTYSIZE (reallocation size for terminal buffers) from 100 to 8191.

Increased MAXDEPTH (maximum depth of input stack) from 10 to 255.

Increased interactive input buffer size from 1024 to 256k.  This has the
effect of increasing the maximum length of an input line from a tty.
This helps with an interactive bug that was reported by Ruslan Kabatsayev
(b7 dot 10110111 at gmail dot com).