implement caching the rendered text and a function to test if rendering
was succesful or not (does_render)
add caching and does_render unittests
remove the does_render method, now main methods get_text and filewriter
return undef in case of error. stringification will return an empty
string though.
Cleanup pod and add get_text and filewriter methods
rename $rnd variable to $trd (no association with random, and it's
TextRender now anyway)
Merge pull request #56 from stdweird/render_renderable_test

TextRender: cache the rendered text and implement does_render test