title: Adding custom highlighting for project's API function names in Vim
body: <p>How can I add new function names for .c and .h files to be highlighted, similar to this 
                   <a href="https://stackoverflow.com/questions/2464593/custumizing-syntax-highlighting-in-vim">Customizing Syntax Highlighting in Vim</a> but much easier? (as I don't need to color words in 
                   different colors, only in the default color for keywords as defined by my theme).</p>
  
  <p>I need this to add highlighting for function names in a project written in C which has a clearly defined API.</p>
  
  <p>Thanks</p>