Tabs have been expanded to spaces in several files that use mainly spaces for indentation.
The files ctype.asm, stdio.asm, and string.asm consistently use tabs for indentation. The tabs in these files have been left alone, except that a few tabs between sentences in comments were changed to spaces. One space-indented line in stdio.asm was changed to use a tab.
The reverted changes relate mainly to adding a second character position in the putback buffer, but the library with those changes crashes on basic stdio operations like printing a string.
For now, this patch reverts stdio to a working, tested version. If the reverted changes are valuable, they can be fixed and then reintroduced later.
