Initial WASM C API implementation. (WebAssembly#1250)

All tests except `threads` pass.

[wasm2c] Fix realloc check in wasm_rt_grow_memory (WebAssembly#1171)

See issue WebAssembly#1159.

Initial custom annotation support (WebAssembly#1076)

Lex custom annotations, but discard them in the parser. In the future we
should be able to parse some of them, but this is simple and
spec-compliant for now.

[travis] Only run before_deploy script once

[travis] Deploy tools webassembly bucket on GCS

[appveyor] Generate sha256 file for deployment

Not sure this will work.

Update to latest spec testsuite

Require reserved instruction bytes to be one byte (WebAssembly#922)

The spec requires that the reserved bytes in `call_indirect`,
`memory.grow`, and `memory.size` to be one zero byte. This means that we
cannot accept `0x80 0x00`, or other "long" LEB128 encodings of zero.

[appveyor] Another try at getting deploys working

[appveyor] Maybe fix deploy issues