[Format] Add some form of user field metadata to IPC schemas

[asfimport]

Users may wish to use user-defined types that can be represented as some Arrow primitive type. We should design a mechanism (similar to the key-value metadata in Parquet) to make this possible.

Reporter: Wes McKinney / @wesm
Assignee: Julien Le Dem / @julienledem

Related issues:

• Arrow release 0.1 (blocks)

PRs and other links:

• PR

_{Note: This issue was originally created as ARROW-301. Please see the migration documentation for further details.}

[asfimport]

Julien Le Dem / @julienledem:
PR: #154

[asfimport]

Julien Le Dem / @julienledem:
Issue resolved by pull request 154
#154