title: change name of rmarkdown pdf and title from a parameter in render call
body: <p>Here is some R markdown code in a "test_param.Rmd" file:</p>
  
  <pre><code>---
  output: pdf_document
  params:
    number: "1"
  title: `r params$number`
  ---
  
  ```{r setup, include=TRUE}
  
  knitr::opts_chunk$set(echo = TRUE)
  
  ```
  
  ```{r one, include = TRUE}
  
  i = 2
  #data = data.frame(x = c(1,2,3))
  
  #for(i in 1:dim(data)[1]){
  
   # plot(i*1000)
  
  #}
  
  ```
  
  `r params$number`
  </code></pre>
  
  <p>that is called using a .r file here:</p>
  
  <pre><code>library(rmarkdown)
  
  rmarkdown::render("C://Users//me//Desktop//test_param.Rmd", 
                    params = list(number= "1"))
  </code></pre>
  
  <p>I get this error when I run the .r </p>
  
  <pre><code>Error in yaml::yaml.load(enc2utf8(string), ...) : 
    Scanner error: while scanning for the next token at line 4, column 8found character that cannot start any token at line 4, column 8
  </code></pre>
  
  <p>Any idea why?</p>
  
  <p>I am using ``  not '' to do the  title: <code>r params$number</code></p>