Add benchmark for file reader

[sadikovi]

This PR adds benchmark for file reader/record iterator. We test 10k-v2.parquet file. Current results on my machine are:

running 1 test
test record_reader_10k_collect ... bench:  45,931,668 ns/iter (+/- 13,826,371) = 14 MB/s

This benchmark is the first step towards understanding the read performance problem, which is tracked in #140.

This PR depends on #146 work, otherwise it fails with not being able to read fixed length byte arrays.

[sadikovi]

@sunchao could you please review? Thanks!

[coveralls]

Pull Request Test Coverage Report for Build 587

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.449%

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Totals
Change from base Build 580:	0.0%
Covered Lines:	11389
Relevant Lines:	11932

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💛 - Coveralls