Convert between a month name and the equivalent number
For example, converts from 'January' to 1 or vice-versa.
Result = MONTH_CNV( MonthInput, [/UP, /LOW, /SHORT ] )
MonthInput - either a string ('January', 'Jan', 'Decem', etc.) or
an number from 1 to 12. Scalar or array.
UP - if set and if a string is being returned, it will be in all
LOW - if set and if a string is being returned, it will be in all
SHORT - if set and if a string is being returned, only the first
three letters are returned.
If the input is a string, the output is the matching month number.If
an input string isn't a valid month name, -1 is returned.
If the input is a number, the output is the matching month name. The
default format is only the first letter is capitalized.
To get a vector of all the month names:
Names = month_cnv(indgen(12)+1)
Written by: Joel Wm. Parker, SwRI, 1998 Dec 9