replace non-breakable space with regular space

Non-brekable space is 0xc2 0xa0 byte sequence in UTF-8.

To find one:

    $ git grep -I -P '\xc2\xa0'

To replace with regular space:

    $ git grep -l -I -P '\xc2\xa0' | xargs sed -i 's/\xc2\xa0/ /g'

This commit doesn't include changes that will overlap with commit f1c59a91.