Implement median operation

[SanskritFritz]

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[SanskritFritz]

I forgot to update the readme:

The plugin allows you to perform calculations (sum, average, median, minimum, maximum, subtraction, multiplication) on columns or rows of numbers within your Markdown tables.
To trigger a calculation, place a special tag within a table cell.

The tag follows this format: [operation][direction][start:end][currency]

• [operation]: A three-letter code indicating the operation:
  • SUM: Calculates the sum of the values.
  • AVG: Calculates the average of the values.
  • MED: Calculates the median of the values.
  • MIN: Finds the minimum value.
  • MAX: Finds the maximum value.
  • SUB: Subtracts the subsequent values from the first value.
  • MUL: Multiplies all the values together.