minor #78 Move redirection_map from root (WouterJ)

This PR was merged into the 2.7 branch.

Discussion
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Move redirection_map from root

Closes #25

As decided in Slack, `_build` is a nice directory for this file.

@javiereguiluz please handle this as you can reflect this change immediately in the build script

Commits
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8aad9e3 Move redirection_map from root

Author: xabbuh