Remove unused variables from mix test file
Merge pull request #1863 from philss/remove-mix-test-warning

Remove unused variables from mix test file
Reduce the amount of fixture files in mix
Ensure Mix properly recurs rebar subdirs, closes #1862
Remove :compile_path from config and move it to Mix.Project
Add :++, :-- and :** to Macro#binary_op_props
Merge pull request #1866 from parroty/fix

Add :++, :-- and :** to Macro#binary_op_props
Ensure app key is required when getting the compile_path
Extract Mix.ProjectStack from Mix.Server
Move mix configs to app environment and split TasksServer
Do not override builtin type
Compile not ok dependencies on deps.get and deps.update
s/wether/whether
Merge pull request #1867 from christhekeele/fix-macro-env-doc-typo

s/wether/whether
Add is_var/1 for use in typespec guards

Allows you to specify a variable without any type contraints.
Move typespec guards to end of spec

Moves precedence of `when` to be lower than `::`.
Move mix dependencies to _build
Rename fetched to loaded and add a manifest_path
Sinplify mechanism for checking and handling locks

In particular, there is no need to pass :lockfile around deps.
We also remove the umbrella handling from the lock.
Ensure archives work with new _build setup