title: Using broom::tidy on felm result with clustered standard errors
body: <p>I'm trying to extract point estimates and confidence intervals from a panel data model. The following reproduces the error using the canned example from the <code>lfe</code> documentation. The only small change I've made is to cluster standard errors at the firm-level to replicate my issue in <code>est2</code>.</p>
  
  <pre><code>## create covariates
  x &lt;- rnorm(1000)
  x2 &lt;- rnorm(length(x))
  
  ## individual and firm
  id &lt;- factor(sample(20,length(x),replace=TRUE))
  firm &lt;- factor(sample(13,length(x),replace=TRUE))
  
  ## effects for them
  id.eff &lt;- rnorm(nlevels(id))
  firm.eff &lt;- rnorm(nlevels(firm))
  
  ## left hand side
  u &lt;- rnorm(length(x))
  y &lt;- x + 0.5*x2 + id.eff[id] + firm.eff[firm] + u
  
  ## estimate and print result
  est1 &lt;- felm(y ~ x+x2| id + firm)
  summary(est1)
  
  ## estimate and print result with clustered std errors
  est2 &lt;- felm(y ~ x+x2| id + firm | 0 | firm)
  summary(est2)
  </code></pre>
  
  <p>I can tidy in the non-clustered SE version or <em>without</em> including the fixed effects:</p>
  
  <pre><code>tidy(est1)
  tidy(est2)
  tidy(est1, fe = TRUE)
  </code></pre>
  
  <p>But I can't if I ask for the fixed effects:</p>
  
  <pre><code>tidy(est2, fe = TRUE)
  </code></pre>
  
  <p>The error is this: <code>Error in overscope_eval_next(overscope, expr) : object 'se' not found</code></p>
  
  <p>I'm not sure if this is a <code>broom</code> side problem or an <code>lfe</code> side problem. It is possible I'm doing something wrong, but there should be point estimates and standard errors for the fixed effects whether or not I cluster the SEs. (And the fact that there are fewer clusters than FEs is probably an econometric issue, but it doesn't seem to be driving this particular problem.) Any suggestions?</p>