[Python] Support _metadata or _common_metadata files when reading Parquet directories

[asfimport]

This should go in before 0.2

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

Related issues:

• Arrow 0.3 release (blocks)
• [C++] Change arrow::FileWriter API to be initialized from a Schema, and provide for writing multiple tables (is blocked by)

_{Note: This issue was originally created as ARROW-528. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
@xhochy I made this not a blocker as I don't have the immediate ability to generate such datasets

[asfimport]

Wes McKinney / @wesm:
PR: #539

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 539
#539