Workaround "bug" in `load-theme`

If you have `php-mode-coding-style` set and you run `load-theme`, it
calls `php-mode-custom-coding-style-set` from
`custom-theme-recalc-variable`.  This happens regardless of what type
of buffer you are in, so if you are in a buffer whose major mode is
not based on `cc-mode`, you can get an error like this:

> Debugger entered--Lisp error: (error "Buffer  *temp* is not a CC Mode buffer (c-set-style)")
>   signal(error ("Buffer  *temp* is not a CC Mode buffer (c-set-style)"))
>   error("Buffer %s is not a CC Mode buffer (c-set-style)" " *temp*")
>   c-set-style("symfony2")
>   php-enable-symfony2-coding-style()
>   php-mode-custom-coding-style-set(php-mode-coding-style symfony2)
>   custom-theme-recalc-variable(php-mode-coding-style)
>   enable-theme(user)
>   enable-theme(solarized-dark)
>   load-theme(solarized-dark)
>   eval((load-theme (quote solarized-dark)) nil)
>   eval-last-sexp-1(nil)
>   eval-last-sexp(nil)
>   call-interactively(eval-last-sexp nil nil)

 This patch makes `php-mode-custom-coding-style-set` check to make
 sure it's in a `php-mode` buffer.

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Be nice to PSR standards (there should be 4 spaces)

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Added myself as contributor

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
README: Reword the mention of Web Mode for clarity

Saying the mode ‘complements’ PHP Mode makes it sound as if the two
can work together, but since they are both major modes that is not
really accurate.  Instead it is better to call Web Mode a great
‘alternative’ to PHP Mode when editing files that contain a lot of
HTML and other markup alongside PHP code.

GitHub-Issue: 107