fexists added

spec/08.standard_library.tex

@@ -87,6 +87,8 @@ is automatically open and closed within the call.}
 \descr{\lstinline|fun fwrite (fname, contents)|}{Writes a file. The arguments are file name and the contents to write as strings. The file
 is automatically created and closed within the call.}
 
+\descr{\lstinline|fun fexists (fname)|}{Checks if a file exists. The argument is the file name.}
+
 \descr{\lstinline|fun fprintf (file, fmt, ...)|}{Same as "\lstinline|printf|", but outputs to a given file. The file argument should be that acquired
   by \lstinline|fopen| function.}