Improvements to Modules API (#307)

* test-no_std: use cargo +nightly

assume folks have rustup set to use stable by default

* cretonne-module, -faerie, -simplejit: use new ModuleError enum

CtonError is not really appropriate for use in the module system.
Instead, create a new enum ModuleError, which implements failure::Fail
(works with no_std). Translate existing panics and unimplemented
error cases to return ModuleErrors.

* cretonne-faerie: export FaerieProduct

* cretonne-module: expose FuncOrDataId, and Module::get_name to lookup

This is helpful for looking up a name that has already been declared.
Also, implement FuncOrDataId -> ExternalName conversion.

* cretonne-faerie: depend on faerie 0.3.0

which has bugfix for data relocations

* cretonne-module: change InvalidDefinition to InvalidImportDefinition

per dan's code review. plus another typo fix

* cretonne-faerie: add optional manifest of all traps from codegen

* cretonne-module: provide more context in panics

* cretonne-faerie: updates to docs

* cretonne-faerie: return an Err instead of debug_assert when isa not pic

lib/module/Cargo.toml

@@ -12,6 +12,7 @@ readme = "README.md"
 cretonne-codegen = { path = "../codegen", version = "0.6.0", default-features = false }
 cretonne-entity = { path = "../entity", version = "0.6.0", default-features = false }
 hashmap_core = { version = "0.1.4", optional = true }
+failure = "0.1.1"
 
 [features]
 default = ["std"]