lexers/r: Match keywords prior to functions

[heavywatal]

Keywords like function, for, if, and return followed by parentheses were recognized as NameFunction; others like in were recognized as normal Name. This PR moves the rule for keywords to the top.

The code tested with go run . in cmd/chromad:

printeven = function(n) {
  for (i in seq_len(n)) {
    if (i %% 2 == 0) {
      print(i)
    }
  }
  return(invisible(n))
}

the original result:

<pre class="chroma"><code><span class="line"><span class="cl"><span class="n">printeven</span> <span class="o">=</span> <span class="nf">function</span><span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nf">for </span><span class="p">(</span><span class="n">i</span> <span class="n">in</span> <span class="nf">seq_len</span><span class="p">(</span><span class="n">n</span><span class="p">))</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nf">if </span><span class="p">(</span><span class="n">i</span> <span class="o">%%</span> <span class="m">2</span> <span class="o">==</span> <span class="m">0</span><span class="p">)</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nf">print</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="nf">return</span><span class="p">(</span><span class="nf">invisible</span><span class="p">(</span><span class="n">n</span><span class="p">))</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span>
</span></span></code></pre>

this PR:

<pre class="chroma"><code><span class="line"><span class="cl"><span class="n">printeven</span> <span class="o">=</span> <span class="kr">function</span><span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="kr">for</span> <span class="p">(</span><span class="n">i</span> <span class="kr">in</span> <span class="nf">seq_len</span><span class="p">(</span><span class="n">n</span><span class="p">))</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="kr">if</span> <span class="p">(</span><span class="n">i</span> <span class="o">%%</span> <span class="m">2</span> <span class="o">==</span> <span class="m">0</span><span class="p">)</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nf">print</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="kr">return</span><span class="p">(</span><span class="nf">invisible</span><span class="p">(</span><span class="n">n</span><span class="p">))</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span>
</span></span></code></pre>

[alecthomas]

Thanks!