[C] Update README and adding object.c/h files

[zhemant]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh, ./bin/security/{LANG}-petstore.sh and ./bin/openapi3/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

• update handling of reserved keywords to make it same in all cases
• update README mustache to give info about how to compile the library and use the library
• add object header and body mustache to create object models
• set isEnum which is required for handling enum variables in C codegen in CLibCurlClientCodegen.java to avoid conflict with other codegen

cc
@wing328

[wing328]

@zhemant can you please rebase this PR on the latest master (which has the travis ci issue addressed)? Let me know if you need help on that.

[wing328]

Overall it looks good but I've not tested it myself. The CI test is good.