add RPC-error-handling(ja)
add RPC-error-handling(en)
rpc-error-workaround(en): fix toc, typo and code snippets
rpc-error-workaround(ja): fix toc and code snippets
move RPC-err-handling to under documentation page
Merge pull request #56 from y-oda-oni-juba/feature/rpc-err-workaround

add RPC-error handling pages