cal: implement -m

Some people prefer the week to start on Monday.  Add the '-m'
option to support this.

function                                             old     new   delta
cal_main                                             926     966     +40
day_array                                            316     337     +21
packed_usage                                       34151   34158      +7
.rodata                                            99224   99225      +1
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(add/remove: 0/0 grow/shrink: 4/0 up/down: 69/0)               Total: 69 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed