Split invalid characters test
Add magic comment US-ASCII

Default source encoding is changed to UTF-8. (was US-ASCII)
Add comment
Remove unnecessary prepare data
Add ascii-8bit modifier to regexp
Revert "Add ascii-8bit modifier to regexp"

This is not for this problem
This reverts commit 341fd4b8b6d737348471233d0f1aafa76dbf30a1.
Merge remote-tracking branch 'origin/master' into fix/split-ascii-8bit
Merge pull request #786 from sanemat/fix/split-ascii-8bit

Extract invalid characters in UTF-8 to other test file