Fix COUNTBLANK for invalid ranges (#732) ...

* * Do not split string into chars when returning enumerator

* Fix test for CountBlank
* Simplify COUNTBLANK evaluation

* Unnecessary check removed. Code auto-formatted. Test for missing arguments added.

Correctly treat DateTime value as number in tallies.

Fix for Issue with SumIf on "full columns" range #646 (#647) ...

* Managed SumIf on string with spaces and applied evaluation of values only when condition is satisfied (resolve "recursion" problem due to use SumIf formula in same range for values).

* Sample application for issue tracking

* Developed requested changes for pull request #647

* Removed sample project in wrong place

* Required changes

* Merge reset

* Removed undesired blank line

* Removed tab

SUMPRODUCT: Blank cells and cells with text should be treated as zeros

Merge pull request #586 from igitur/ExcelNumberFormat ...

Use ExcelNumberFormat library to format strings.

Upgrade ExcelNumberFormat to v1.0.3 and re-enable test

Use ExcelNumberFormat library for Text() function too

separate test cases for FLOOR.MATH ...

this would allow easier detection of what's failing and follows the principle of one assertion per test.

improve FACTDOUBLE and add unit tests ...

FACTDOUBLE now throws correct exceptions and

improve Fact (throw correct exceptions on invalid input), add unit tests

add unit test for EXP function

unit tests for EVEN

unit tests for DEGREES function

add unit testeds for COSH

add unit tests for COS

improve COMBIN and add unit tests ...

COMBIN did not handle non-numeric values correctly. Should throw NumberException (#NUM in Excel). Returned 0 for any non-numeric parameter instead before

implement BASE and corresponding unit tests

throw correct exceptions on ATANH and add unit tests

fix ATAN2 implementation and add tests ...

Math.Atan2() expects y as first parameter and x as second, while in Excel x is first,
throw "correct" exception on input (0, 0)

add unit tests

add unit tests for ATAN function

add unit tests for ASINH

improve ASIN: throw NumberException for values not in range for Excel ...

...add unit tests for ASIN

implement ARABIC and unit tests

restrict valid input range to [1..) as in Excel, add unit tests.

fix ACOS implementation: in Excel only defined in range [-1, 1] ...

if input is not in range, throw exception.

adding unit tests for ACOS

ABS was implemented already, adding unit tests.

implement SECH function and corresponding tests

implement SEC and corresponding unit tests

implement ACOTH function and corresponding unit tests

implement ACOT function and unit tests