* ale.txt: fix indentation
* ale.txt: fix Type and Default markup
* ale.txt: use `not set` instead of `undefined`
This matches the way the variables are referenced in prose about
existence state.
Typically proto files depend on and make use of proto definitions in
other files. When invoking protoc user can supply paths to inspect for
dependencies.
This patch makes it possible to configure flags passed to protoc. This
makes it e.g., possible to change include paths of the linter's protoc
invocation.
