Add configuration parsing to the public API.

Don't remove it from the extension API for now - to match the value
packing code. Updated inline documentation, but not the official
documentation - since I suspect this will change before it's merged.
Update wtperf usage of configuration parsing API.
Add ability for wtperf to run with multiple databases in different threads.

This can be handy when testing shared cache behavior or generating different
I/O workloads.
Merge branch 'develop' into config-parse-api
Merge branch 'config-parse-api' into wtperf-multiple-databases
Update the configuration parsing API. Not finalized, but a step closer.
Skip measuring the very first operation to avoid severe latency spike
measurements.
Move latency measurement on populate with multiple tables.
Update the configuration parsing API. Including:

* Don't copy the input string.
* Remove reset and remove complex semantics.
* Rename search back to get.
Add in an example for querying a nested value.
Configuration parser API, update documentation and examples.
Fix example code return value.
Update the configuration string parsing in Helium data source.
Simplify code to always use the cfg->uris array.
Fix warning.
Fix stat Options subsection.
When multiple tables are configured, spread the data.
Typo.
Fix compiler warnings re: ignored return values.
Add wiredtiger_config_parser_open and wiredtiger_version into extension API.

This is necessary so that statically linked applications can always
find the symbols.
Merge branch 'develop' into config-parse-api

Conflicts:
	src/include/wiredtiger_ext.h