title: R Installing prior verison package NAMESPACE file missing
body: <p>I'm using Windows and is trying to install latentnet package in version 2.1.1. You can locate the package in the following link:</p>
  
  <p><a href="https://cran.r-project.org/src/contrib/Archive/latentnet/latentnet_2.1-1.tar.gz" rel="nofollow noreferrer">https://cran.r-project.org/src/contrib/Archive/latentnet/latentnet_2.1-1.tar.gz</a></p>
  
  <p>I tried to use:</p>
  
  <pre><code>    install_version("latentnet", version = "2.1-1", repos = "http://cran.us.r-project.org")
  </code></pre>
  
  <p>Error message received:</p>
  
  <pre><code>Downloading package from url: http://cran.us.r-project.org/src/contrib/Archive/latentnet/latentnet_2.1-1.tar.gz
  WARNING: Rtools is required to build R packages, but no version of Rtools compatible with R 3.5.1 was found. (Only the following incompatible version(s) of Rtools were found:3.5)
  
  Please download and install the appropriate version of Rtools from http://cran.r-project.org/bin/windows/Rtools/.
  Installing latentnet
  "C:/Program Files/R/R-3.5.1/bin/x64/R" --no-site-file --no-environ --no-save --no-restore --quiet  \
    CMD INSTALL "C:/Users/wawa0001/AppData/Local/Temp/RtmpCig4et/devtools504261651b3/latentnet"  \
    --library="C:/Users/wawa0001/Documents/R/win-library/3.5" --install-tests 
  
  * installing *source* package 'latentnet' ...
  ERROR: a 'NAMESPACE' file is required
  * removing 'C:/Users/wawa0001/Documents/R/win-library/3.5/latentnet'
  In R CMD INSTALL
  </code></pre>
  
  <p>Then I tried to download the package to my local drive and used following command:</p>
  
  <pre><code>install.packages("latentnet_2.1-1.tar.gz", repos = NULL)
  </code></pre>
  
  <p>I received another error message:</p>
  
  <pre><code>Installing package into �C:/Users/wawa0001/Documents/R/win-library/3.5�
  (as �lib� is unspecified)
  * installing *source* package 'latentnet' ...
  ERROR: a 'NAMESPACE' file is required
  * removing 'C:/Users/wawa0001/Documents/R/win-library/3.5/latentnet'
  * restoring previous 'C:/Users/wawa0001/Documents/R/win-library/3.5/latentnet'
  In R CMD INSTALL
  Warning in install.packages :
    installation of package ‘latentnet_2.1-1.tar.gz’ had non-zero exit status
  </code></pre>
  
  <p>It seems I need to create a 'NAMESPACE' file, and I referred to this post:
  <a href="https://stackoverflow.com/questions/17196225/error-a-namespace-file-is-required">ERROR: a &#39;NAMESPACE&#39; file is required</a></p>
  
  <p>However, command <code>tar</code> does not exist on my PC externally or internally and I do not know a way to get it to execute. </p>
  
  <p>Could anyone suggest a way to download the early version of the package? I currently have R 3.4.4.</p>
  
  <p>Thanks!</p>