Improve code formatting in the README
Improve code formatting in the README

* Use backticks to format code inline instead of asterisks, which are
  interpreted as italics in Markdown
* This helps us remove the `&#42;` HTML entities which were used to
  create asterisks within asterisks-surrounded regions for C pointers,
  making the text much more readable
* Added backticks around filenames and function names in headings, which
  improves readability in the README, and avoids confusing Markdown
  parsers in editors which highlight regions of text as italics
  (underscores also create italicized text) when it is not intended
* Annotate all code samples as C code to get syntax highlighting, making
  code samples much easier to read

google/cmockery,google/cmockery