- Allow empty filter, data, and rows in the pivot table
- Add more test case for pivot table

Resolve #580, revert commit https://github.com/360EntSecGroup-Skylar/excelize/commit/5ca7231ed408ac264f509ff52b5d28ff4fbda757

* #386 regression test added

* closes #386 string to bigint on GOARCH=386

* Rewrite prepareSheetXML to scale linearly

We don't need to backfill columns into every row for most purposes
Provided makeContiguousColumns for setting styles where we do
need it for a specific region.

Added a benchmark to monitor progress. For 50,000 rows this went
from about 11 seconds to 1 second. The improvements are more
dramatic as the row/column count increases.

* Assigning that row value was redundant

Exported functions:

SetCellStyle
InsertCol
RemoveCol
RemoveRow
InsertRow
DuplicateRow
DuplicateRowTo
SetRowHeight
GetRowHeight
GetCellValue
GetCellFormula
GetCellHyperLink
SetCellHyperLink
SetCellInt
SetCellBool
SetCellFloat
SetCellStr
SetCellDefault
GetCellStyle
SetCellValue
MergeCell
SetSheetRow
SetRowVisible
GetRowVisible
SetRowOutlineLevel
GetRowOutlineLevel
GetRows
Columns
SearchSheet
AddTable
GetPicture
AutoFilter
GetColVisible
SetColVisible
GetColOutlineLevel
SetColOutlineLevel
SetColWidth
GetColWidth

inner functions:

adjustHelper
adjustMergeCells
adjustAutoFilter
prepareCell
setDefaultTimeStyle
timeToExcelTime
addDrawingChart
addDrawingVML
addDrawingPicture
getTotalRowsCols
checkRow
addDrawingShape
addTable

This allows the user to set a floating point value into a
cell with a specific number of places after the decimal.

Closes #357

* Huge refactorig for consistent col/row numbering

Started from simply changing ToALphaString()/TitleToNumber() logic and related fixes.
But have to go deeper, do fixes, after do related fixes and again and again.

Major improvements:

1. Tests made stronger again (But still be weak).
2. "Empty" returns for incorrect input replaces with panic.
3. Check for correct col/row/cell naming & addressing by default.
4. Removed huge amount of duplicated code.
5. Removed ToALphaString(), TitleToNumber() and it helpers functions at all,
and replaced with SplitCellName(), JoinCellName(), ColumnNameToNumber(), ColumnNumberToName(), CellNameToCoordinates(), CoordinatesToCellName().
6. Minor fixes for internal variable naming for code readability (ex. col, row for input params, colIdx, rowIdx for slice indexes etc).

* Formatting fixes

Primary motivation: Avoid statefull tests with not ignorable git file tree changes.
Multiple tests reads and overwrites signle file for won needs.
Multiple tests reads and overwrites file under version control.

Secondary motivation: Minimal tests logic aligment, separate error expectation
and not error expectation tests. Introduce sub-test over test data sets and so far.

This commit is not ideal but necessary (IMHO)

- Fix ineffectual assignments in Go code;
- Godoc has been updated

make SetCellStyle quicker by skipping conversions in checkCellInArea, and skipping area checks when we are sure the cell can't be before or past the current row/col
Signed-off-by: Matthieu Bresson