More benchmarks.

Add a hand-rolled maps line parser as something to compare our realistic
sscanf benchmark against. Also add benchmarks for the ato*/strto* family.

This patch doesn't fix the tests, which seem to have been broken by
the recent google-benchmark upgrade despite the benchmarks themselves
all working just fine. To me that's a final strike against these tests
which are hard to maintain and not obviously useful, but we can worry
about what to do with them -- whether to just delete them or to try to
turn them into tests that actually have some value -- in a separate CL.

Bug: N/A
Test: ran benchmarks
Change-Id: I6c9a77ece98d624baeb049b360876ef5c35ea7f2