Support Hidden Row, Hidden Column, Active Sheet, Hidden Sheet, Tab Color

Prevent exceptions in get_row_heights, get_col_widths if array ref never materialized in hash (none have non-std width)

Add emacs backup files to .gitignore
Prevent color palette from leaking from one workbook to another.

Deprecates S:P:E ColorIdxToRGB - will return value for last workbook opened, which is the best we can do.

Replacement is $workbook->ColorIdxToRGB, which always should get it right.
Test case for get_active_sheet
Rename workbook version of ColorIdxToRGB to color_idx_to_rgb

Add tests for color_idx_to_rgb, get_tab_color, is_sheet_hidden, is_row_hidden, is_col_hidden.
Switch variables in new code to lowercase without datatype prefixes per guidance from JMM
Merge remote-tracking branch 'tlhackque/master' into from_tlhackque

Conflicts:
	.gitignore
Add to Changes file

List changes and reference RT