Add :history_size option to IEx
Fix v helper to work with new :iex_history format
Document :history_size option
Don't reverse v's output
s/less than 0/negative/
Handle rebar dependencies better

Download dependencies specified in rebar.config and go through
Converger to handle conflicts.
Handle `sub_dirs` in rebar.config when getting dependencies and
by the sub_dirs to the code load path.
Handle raw option in rebar deps
Extract history management in its own module
Make IEx helpers use inspect_opts where appropriate

For instance, the v helper would print the results in their entirety
ignoring the "limit" option.
Use just the process dictionary for keeping history
Minor code formatting fix
Inline nillify in Process
Implement the heuristics for garbage collection
Allow keywords in typespecs
Merge pull request #1121 from alco/iex-limit-history

Iex limit history
Remove unused variable warning
Update CHANGELOG
Error if guards are given but no implementation, closes #1125
Add tests for body-less functions
Merge pull request #1126 from alco/1125-test

Add tests for body-less functions