initial commit
Create LICENSE.md
Added lexing logic for arrays {1,2,3}

basically it's just an alias for () afaik.
Added lexing logic for references where references are looked up
right before evaluation, and not when pushing to valueStack.

also correctly implemented ISNUMBER and SUM and their tests.
Added ISREF function, in the prosess, merged excel-functions.js and lexer.js
renamed to efp(-test).js and moved some code around.

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Added ISERR,ISERROR functions

as a result, extended SUM to correctly handle erronous input.
Added AVERAGE and AVERAGEA functions
Added COUNTIF
cleaned up some code.
doing some refactoring to distingish between data types
Refactored the way arrays and parenthesis groups were lexed
Added COUNT,ISTEXT functions
Added PERCENTILE function
Added input validation to PERCENTILE
Added RANDBETWEEN
Renamed test suite
Merge branch 'master' into gh-pages