bmp2c64: check for inverted bitmap

top left pixel in bitmap is now used as a reference for a 0
should be configurable in future
Makefile fix: ignore non-fatal errors

ignore building errors for tools/* and generated source files, so
an existing generated source file can be used for successfull build
some font tweaks for readability

sacrifice some original topaz resemblance for better readability.
Affected glyphs: a (including all accented versions), D, S, 1, 4, 6, 9