stbt.py, stbt-templatematch: Reword "Weak match" to "No match"

For someone who is not familiar with the template match algorithm,
the log message "Weak match found" when the match gets through
the first pass but doesn't get through the second pass is misleading.

Reword the log message to
"No match found. Closest match: MatchResult(...)"
if no match found.

The message is the same
"Match found: MatchResult(...)"
if the template matches the screenshot.
stbt-templatematch: Do not print "match=True" if there is no match

stbt-templatematch incorrectly prints
"MatchResult(timestamp=0, match=True, ...)"
even if the template did not match the screenshot.

Print "match=False" in this case.
Merge remote-tracking branch 'szemate/reword-weak-match'

* szemate/reword-weak-match:
  stbt-templatematch: Do not print "match=True" if there is no match
  stbt.py, stbt-templatematch: Reword "Weak match" to "No match"
README.rst: Update subtitle to match description on stb-tester.com

I made a similar change to the description of the RPM package in
commit fde36144.