[Python] Add function to compute the total size of tensor payloads, including metadata and padding

[asfimport]

This will be useful for ensuring that memory maps have enough space available to write out a data structure

cc @pcmoritz @robertnishihara

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

Related issues:

• Arrow 0.3 release (blocks)

_{Note: This issue was originally created as ARROW-761. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
PR: #521

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 521
#521