perf diff: don't compute Delta if he->dummy

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf diff: give Delta column an appropriate color

Colorize the numbers in the Delta column either green or red depending
on whether the it is positive or negative.

Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf diff: generalize hpp__color_delta for -c

Generalize the function so that we can accommodate all three comparison
methods: delta, ratio, and wdiff.

Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf diff: give Ratio column an appropriate color

In

  $ perf diff -c ratio

color the Ratio column using percent_color_snprintf().

Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>