Add bash completion for truffle commands

[LogvinovLeon]

• I've asked for help in the Truffle Gitter before filing this issue.

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Issue

truffle does not support bash completion

Steps to Reproduce

truffle ver<Tab>

Expected Behavior

truffle ver<Tab> -> truffle version

Actual Results

truffle ver<Tab> -> truffle ver

Environment

• Operating System: macos
• Truffle version: 3.1.1
• Ethereum client: N/A
• node version: N/A
• npm version: N/A

[tcoulter]

Tab completion is a environment-specific feature and exists outside of the Truffle executable itself. Instead of supporting just bash, we'll instead add short-letter aliases for existing commands. See #491.