Fix typos and unify wordings in readme
Fix typos and unify wordings in readme

Fixes some typos and wording as well as formatting inconsistencies. Clarifies some small points.
ikesyo/ObjectMapper,tonyli508/ObjectMapperDeep,Busta117/ObjectMapper,tonyli508/ObjectMapperDeep,Hearst-DD/ObjectMapper,cfraz89/ObjectMapper,cfraz89/ObjectMapper,Hearst-DD/ObjectMapper,Busta117/ObjectMapper,ikesyo/ObjectMapper