Add kj-http to cmake build.

Apparently the test has accidentally been using the installed capnp all along.

Fixes #196

Bug fix rollup for 0.6 release

Fixes #212

Specifically, consider:

    capnp::BuilderFor<capnp::DynamicStruct> capnp::Orphan<capnp::AnyPointer>::getAs<capnp::DynamicStruct>(capnp::StructSchema)

Note that `BuilderFor` is a "template using" directive which expands into something more complicated.

GCC mangles the symbol as:

    _ZN5capnp6OrphanINS_10AnyPointerEE5getAsINS_13DynamicStructEEENS_11BuilderFor_IT_Xcl4kindIS6_EEEE4TypeENS_12StructSchemaE

Which `c++filt` decodes as:

    capnp::BuilderFor_<capnp::DynamicStruct, (kind<capnp::DynamicStruct>)()>::Type capnp::Orphan<capnp::AnyPointer>::getAs<capnp::DynamicStruct>(capnp::StructSchema)

Note that `BuilderFor_<...>::Type` here ends up being a typedef for `DynamicStruct::Builder`. It seems weird to me that the symbol name would not substitute this typedef.

Clang, meanwhile, mangles the symbol as:

    _ZN5capnp6OrphanINS_10AnyPointerEE5getAsINS_13DynamicStructEEENS_11BuilderFor_IT_Xclgssr5capnpE4kindIS6_EEEE4TypeENS_12StructSchemaE

Which `c++filt` does not seem to be able to demangle at all. But, it looks like `capnp::kind` is in there, suggesting that, again, the typedef wasn't substituted.

I don't know who is right, but if we inline the whole thing, the problem goes away.

Fixes #251

Fixes #336

Fixes #363.

Fixes #403

Fixes #405

Fixes #435

Fixes #456

Configure Travis CI for Linux and OSX builds.

This is redundant since branches are usually open in order to become PRs, which get their own merged-with-master builds.

I think this is worthwhile since otherwise this header can't be used at all on MSVC, which has all sorts of sad downstream effects. Hopefully we can revert this soon, when MSVC gets fixed.

fix typo in comment

Fix bug where struct equality could ignore some pointer fields.

fix copy-pasto in recently-added test case

update method names in error messages

Fixes #174

adjust AnyList::equals(): a list of pointers cannot be equal to a struct list

I did run them once and they passed. It took a very long time.