Use the builtin envvar role for env vars

Also fix some broken links

docs/conf.py

@@ -103,9 +103,9 @@ rst_prolog = '''
 .. role:: bold
 .. role:: cyan
 .. role:: title
-.. role:: env
 
 '''.replace('VERSION', str_version)
+nitpicky = True
 
 
 # -- Options for HTML output -------------------------------------------------

docs/launch.rst

@@ -42,7 +42,7 @@ The piping environment
 --------------------------
 
 When using :option:`launch --stdin-source`, the program to which the data is
-piped has a special environment variable declared, :env:`KITTY_PIPE_DATA` whose
+piped has a special environment variable declared, :envvar:`KITTY_PIPE_DATA` whose
 contents are::
 
    KITTY_PIPE_DATA={scrolled_by}:{cursor_x},{cursor_y}:{lines},{columns}