Create temporary cache files in Dir.tmpdir (#459)

* OctoFetcher: http_cache options conditional
* Locate cache directory using Dir.tmpdir
* Cache files options can not have defaults

man/git-generate-changelog.1

@@ -1,7 +1,7 @@
 .\" generated with Ronn/v0.7.3
 .\" http://github.com/rtomayko/ronn/tree/0.7.3
 .
-.TH "GIT\-GENERATE\-CHANGELOG" "1" "November 2016" "" ""
+.TH "GIT\-GENERATE\-CHANGELOG" "1" "December 2016" "" ""
 .
 .SH "NAME"
 \fBgit\-generate\-changelog\fR \- Generate changelog from github
@@ -256,13 +256,13 @@ Use HTTP Cache to cache Github API requests (useful for large repos) Default is
 \-\-[no\-]cache\-file [CACHE\-FILE]
 .
 .P
-Filename to use for cache\. Default is /tmp/github\-changelog\-http\-cache
+Filename to use for cache\. Default is github\-changelog\-http\-cache in a temporary directory\.
 .
 .P
 \-\-cache\-log [CACHE\-LOG]
 .
 .P
-Filename to use for cache log\. Default is /tmp/github\-changelog\-logger\.log
+Filename to use for cache log\. Default is github\-changelog\-logger\.log in a temporary directory\.
 .
 .P
 \-\-[no\-]verbose

man/git-generate-changelog.1.html

@@ -246,11 +246,11 @@
 
 <p>   --[no-]cache-file [CACHE-FILE]</p>
 
-<p>   Filename to use for cache. Default is /tmp/github-changelog-http-cache</p>
+<p>   Filename to use for cache. Default is github-changelog-http-cache in a temporary directory.</p>
 
 <p>   --cache-log [CACHE-LOG]</p>
 
-<p>   Filename to use for cache log. Default is /tmp/github-changelog-logger.log</p>
+<p>   Filename to use for cache log. Default is github-changelog-logger.log in a temporary directory.</p>
 
 <p>   --[no-]verbose</p>
 
@@ -281,7 +281,7 @@
 
   <ol class='man-decor man-foot man foot'>
     <li class='tl'></li>
-    <li class='tc'>November 2016</li>
+    <li class='tc'>December 2016</li>
     <li class='tr'>git-generate-changelog(1)</li>
   </ol>
 

man/git-generate-changelog.md

@@ -173,11 +173,11 @@ Automatically generate change log from your tags, issues, labels and pull reques
 
    --[no-]cache-file [CACHE-FILE]
 
-   Filename to use for cache. Default is /tmp/github-changelog-http-cache
+   Filename to use for cache. Default is github-changelog-http-cache in a temporary directory.
 
    --cache-log [CACHE-LOG]
 
-   Filename to use for cache log. Default is /tmp/github-changelog-logger.log
+   Filename to use for cache log. Default is github-changelog-logger.log in a temporary directory.
 
    --[no-]verbose