* Implement wasm trap handlers.
This adds signal handlers based on SpiderMonkey's signal-handler code.
The functionality for looking up the trap code and wasm bytecode offset
isn't yet implemented, but this is a start.
I considered rewriting this code in Rust, but decided against it for now
as C++ allows us to talk to the relevant OS APIs more directly.
Fixes#15.
* Compile with -std=c++11.
* Refactor InstallState initialization.
* Compile with -fPIC.
* Factor out the code for calling a wasm function with a given index.
* Fix unclear wording in a comment.
