[Rust] Move calls to free() into memory.rs

[asfimport]

We had calls to free memory in a few places, with duplication of effort for Windows support. This PR simply creates a free_aligned() method in memory.rs so we have all memory alloc/free and Windows references in a single file.

Reporter: Andy Grove / @andygrove
Assignee: Andy Grove / @andygrove

PRs and other links:

• GitHub Pull Request #1919

_{Note: This issue was originally created as ARROW-2481. Please see the migration documentation for further details.}

[asfimport]

Uwe Korn / @xhochy:
Issue resolved by pull request 1919
#1919