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/faerie/src/traps.rs

@@ -0,0 +1,64 @@
+//! Faerie trap manifests record every `TrapCode` that cretonne outputs during code generation,
+//! for every function in the module. This data may be useful at runtime.
+
+use cretonne_codegen::{ir, binemit};
+
+/// Record of the arguments cretonne passes to `TrapSink::trap`
+pub struct FaerieTrapSite {
+    /// Offset into function
+    pub offset: binemit::CodeOffset,
+    /// Source location given to cretonne
+    pub srcloc: ir::SourceLoc,
+    /// Trap code, as determined by cretonne
+    pub code: ir::TrapCode,
+}
+
+/// Record of the trap sites for a given function
+pub struct FaerieTrapSink {
+    /// Name of function
+    pub name: String,
+    /// Total code size of function
+    pub code_size: u32,
+    /// All trap sites collected in function
+    pub sites: Vec<FaerieTrapSite>,
+}
+
+
+impl FaerieTrapSink {
+    /// Create an empty `FaerieTrapSink`
+    pub fn new(name: &str, code_size: u32) -> Self {
+        Self {
+            sites: Vec::new(),
+            name: name.to_owned(),
+            code_size,
+        }
+    }
+}
+
+impl binemit::TrapSink for FaerieTrapSink {
+    fn trap(&mut self, offset: binemit::CodeOffset, srcloc: ir::SourceLoc, code: ir::TrapCode) {
+        self.sites.push(FaerieTrapSite {
+            offset,
+            srcloc,
+            code,
+        });
+    }
+}
+
+/// Collection of all `FaerieTrapSink`s for the module
+pub struct FaerieTrapManifest {
+    /// All `FaerieTrapSink` for the module
+    pub sinks: Vec<FaerieTrapSink>,
+}
+
+impl FaerieTrapManifest {
+    /// Create an empty `FaerieTrapManifest`
+    pub fn new() -> Self {
+        Self { sinks: Vec::new() }
+    }
+
+    /// Put a `FaerieTrapSink` into manifest
+    pub fn add_sink(&mut self, sink: FaerieTrapSink) {
+        self.sinks.push(sink);
+    }
+}