Improve performance parsing quoted attributes

[odlp]

Whilst benchmarking a Rails app with memory bloat issues, I noticed a small improvement which could be made to Parser#parse_attributes

Changes:

• Adds static quoted attributes to the .slim / .haml / .erb benchmark templates.
• Moves creation of splat prefix regex to the Parser initialization, rather than each invocation of Parser#parse_attributes.

Local benchdiff results:

                    user     system      total        real
------------------------------------------------------Parse
After patch:    2.650000   0.010000   2.660000 (  2.660088)
Before patch:   2.930000   0.010000   2.940000 (  2.936652)
Improvement: 9%

-----------------------------------------------------Render
After patch:    0.840000   0.000000   0.840000 (  0.840143)
Before patch:   0.840000   0.000000   0.840000 (  0.838565)
Improvement: 0%