Output warning in JSON generator if an unmatched argument is found in descriptor.json

[rcjsuen]

When making additions or changes to NodeGit to match libgit2, we have to make changes to the generate/input/descriptor.json file. If we make a typo, it goes completely undetected until your test code fails or you when you manually inspect the generated C++ code. To make this feedback loop better, we should generate a warning if an argument name used in the descriptor does not match the name
in the C function. This fixes #1464 and will make everyone's lives a lot easier when adding new API to NodeGit.

The following is the new output from Travis CI.

[nodegit] Running pre-install script
[nodegit] Configuring libssh2.
[nodegit] Checking submodule status
[nodegit] Initializing submodules
[nodegit] Generating native code
Found non-matching argument named flags in descriptor.json for C function git_index_remove_all
Found non-matching argument named flags in descriptor.json for C function git_index_update_all
Found non-matching argument named force in descriptor.json for C function git_index_write
Found non-matching argument named signature in descriptor.json for C function git_rebase_init
Found non-matching argument named signature in descriptor.json for C function git_branch_create
Found non-matching argument named log_message in descriptor.json for C function git_branch_create
Found non-matching argument named log_message in descriptor.json for C function git_reset
Found non-matching argument named signature in descriptor.json for C function git_reset
Found non-matching argument named return in descriptor.json for C function git_status_file
[nodegit] Running install script