Option to disable writing title

[jayvdb]

TextSheetWriter.__init__ always emits "Sheet Name: %s\n" % name to the file. When the source is a CSV, name is the filename.

For a single sheet book the sheet name is typically unnecessary, and this part of the file will typically break the file format.

[chfw]

'single_sheet_in_book' is passed on from pyexcel. I will take a look.