Feature/lazy evaluation

[parkervg]

On queries like benchmarks/national_parks/q05.sql:

SELECT {{ImageCaption('parks::Image')}} as "Image Description" FROM parks LIMIT 1

We apply the LIMIT clause (and any other surrounding filters) prior to calling the ImageCaption ingredient

Benchmark Results:

Before:

Task	Average Runtime	# Unique Queries
financials	0.0402491	7
rugby	0.323255	4
national_parks	2.07314	5
1966_nba_draft	0.119926	2

After:

Task	Average Runtime	# Unique Queries
financials	0.040797	7
rugby	0.319473	4
national_parks	0.865904	5
1966_nba_draft	0.115434	2