format-to-string is renamed to sformat

Module: dsp imports format-to-string but renames it to sformat. Some code still tries to use format-to-string.
format-to-string is renamed to sformat

Module: dsp imports format-to-string but renames it to sformat. Some code still tries to use format-to-string.
Merge pull request #60 from kibook/patch-2

format-to-string is renamed to sformat