Add option to exclude or include tweaks

I added (optional) options to allow excluding or including specific tweaks.

Include tweaks using the with option:
```ruby
# single tweak
SvgOptimizer.optimize(xml, with: :remove_comment)           

# multiple tweaks                     
SvgOptimizer.optimize(xml, with: [:remove_comment, :remove_empty_container])
```

Exclude tweaks using the without option:
```ruby
# excluding a single tweak
SvgOptimizer.optimize(xml, without: :remove_comment)

# excluding multiple tweaks
 SvgOptimizer.optimize(xml, without: [:remove_comment, :remove_empty_container])
```