feat(log): enhance cmd highlighter and make it configurable

[antongolub]

This PR:

• enhances formatCmd helper to properly highlight cmds and their params
• separates log module
• makes cmd formatter configurable via log.formatCmd
• makes the default log stream customizable through log.output
• adds missing log() tests

closes #1119

@antonmedv
@stefansundin

Could you plz provide more examples as is vs to be.

• Tests pass
• Appropriate changes to README are included in PR

[stefansundin]

It looks good to me, although I haven't checked out the code to do any testing on my own.

It might be worth checking how these are colored:

echo test > filepath
echo test >> filepath
echo test 2> filepath
echo test &> filepath
echo test &>> filepath
echo test >& filepath
echo 1+2 | bc
bc < filepath

Maybe overly complicated:

cat << 'EOF' | tee -a filepath
line 1
line 2
EOF

[antongolub]