Pylightxl

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- bug-fix: updated encoding for string cells that contained xml-like data (ex: cell A1 "<cell content>")

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- add feature to ``writecsv`` to be able to handle ``pathlib`` object and ``io.StreamIO`` object
- refactored readxl to remove regex, now readxl is all cElementTree
- refactored readxl/writexl to able to handle excel files written by openpyxl that is generated
differently than how excel write files.

- added new function: ``db.nr('table1')`` returns the contents of named range "table1"
- added new function: ``db.ws('Sheet1').range('A1:C3')`` that returns the contents of a range
it also has the ability to return the formulas of the range
- updated ``db.ws('Sheet1').row()`` and ``db.ws('Sheet1').col()`` to take in a new argument ``formual``
that returns the formulas of a row or col
- bugfix: write to existing without named ranges was throwing a "repair" error. Fixed typo on xml for it
and added unit tests to capture it
- added new function: ``xl.readcsv(fn, delimiter, ws)`` to read csv files and create a pylightxl db out
of it (type converted)
- added new function: ``xl.writecsv(db, fn, ws, delimiter)`` to write out a pylightxl worksheet as a csv

- bug fix: added ability to input an empty string into the cell update functions
(previously entering val='') threw and error

- added support for cell values that have multiple formats within a single cell.
previous versions did not support this functionality since it is logged differently in sharedString.xml
- added support for updating formulas and viewing them:

- view formula: ``db.ws('Sheet1').address('A1', formula=True)``
- edit formula: ``db.ws('Sheet1').update_address('A1', val='=A1+10')``

- updated the following function arguments to drive commonality:

- was: ``readxl(fn, sheetnames)`` new: ``readxl(fn, ws)``
- was: ``writexl(db, path)`` new: ``writexl(db, fn)``
- was: ``db.ws(sheetname)`` new: ``db.ws(ws)``
- was: ``db.add_ws(sheetname, data)`` new: ``db.add_ws(ws, data)``

- added new feature to be able to read-in NamedRanges, store it in the Database, update it, remove it,
and write it. NamedRanges were integrated with existing function to handle semi-structured-data

- ``db.add_nr(name'range1', ws='sheet1', address='A1:C2')``
- ``db.remove_nr(name='range1')``
- ``db.nr_names``

- add feature to remove worksheet: ``db.remove_ws(ws='Sheet1')``
- add feature to rename worksheet: ``db.rename_ws(old='sh1', new='sh2')``
- added a cleanup function upon writing to delete _pylightxl_ temp folder in case an error left them
- added feature to write to file that is open by excel by appending a "new_" tag to the file name and
a warning message that file is opened by excel so a file was saved as "new_" + filename

- bug fix: accounted for num2letter roll-over issue
- new feature: added a pylightxl native function for handling semi-structured data
- refactored code to be a single file