[StreamExecutor] Fix KernelSpec Doxygen

[jhen]

Summary

There was a typo where \endcode was spelled as \encode and it was
keeping the whole file document from rendering. I also added in some \c
annotations for inline code stuff to make it look nicer.

[jprice]

Aha, this explains why I couldn't find these classes in the docs yesterday.

streamexecutor/include/streamexecutor/KernelSpec.h

 /// MultiKernelLoaderSpec::addCUDAPTXInMemory can be used to construct and
 /// register a CUDAPTXInMemorySpec KernelLoaderSpec.
 ///
 /// The loader spec classes declared here are designed primarily to be
 /// instantiated by the compiler, but they can also be instantiated directly by
 /// the user. A simplified example workflow which a compiler might follow in the
 /// case of a CUDA kernel that is compiled to CUDA fatbin code is as follows:
 ///
-/// 1. The user defines a kernel function called UserKernel.
+/// 1. The user defines a kernel function called \c UserKernel.
 /// 2. The compiler compiles the kernel code into CUDA fatbin data and embeds
-///    that data into the host code at address __UserKernelFatbinAddress.
+///    that data into the host code at address \c __UserKernelFatbinAddress.
 /// 3. The compiler adds code at the beginning of the host code to instantiate a
 ///    MultiKernelLoaderSpec:
 ///    \code
 ///    namespace compiler_cuda_namespace {
 ///      MultiKernelLoaderSpec UserKernelLoaderSpec;
 ///    } // namespace compiler_cuda_namespace
 ///    \endcode
 /// 4. The compiler then adds code to the host code to add the fatbin data to
 ///    the new MultiKernelLoaderSpec, and to associate that data with the kernel
-///    name "UserKernel":
+///    name \c "UserKernel":
 ///    \code
 ///    namespace compiler_cuda_namespace {
 ///      UserKernelLoaderSpec.addCUDAFatbinInMemory(
 ///        __UserKernelFatbinAddress, "UserKernel");
 ///    } // namespace compiler_cuda_namespace
-///    \encode
+///    \endcode
 /// 5. The host code, having known beforehand that the compiler would initialize
 ///    a MultiKernelLoaderSpec based on the name of the CUDA kernel, makes use
-///    of the symbol cudanamespace::UserKernelLoaderSpec without defining it.
+///    of the symbol \c cudanamespace::UserKernelLoaderSpec without defining it.
 ///
 /// In the example above, the MultiKernelLoaderSpec instance created by the
 /// compiler can be used by the host code to create StreamExecutor kernel
 /// objects. In turn, those StreamExecutor kernel objects can be used by the
 /// host code to launch the kernel on the device as desired.
 ///
 //===----------------------------------------------------------------------===//