vembedr: Embed Video in HTML

adds support for Microsoft Stream, which offers an enterprise video service; this will likely be for use internal to an organization. (#38)
if you have a recent version of usethis installed, suggest_embed() will copy the suggested code to your clipboard. (#32)
sets the default height to 300 pixels, and introduces an argument ratio, to set the aspect ratio; legal values are "16by9" or "4by3". If you set the width and height, ratio is ignored. If you specify only one of width or height, ratio is used to calculate the other. (#33)
adds three functions to help with formatting; they are all pipeable with embed_*() functions:
use_rounded() lets you specify rounded corners. (#25, with @koncina and @ginolhac)
use_align() lets you specify a horizontal alignment.
use_bs_responsive() if your 'HTML' page includes Twitter Bootstrap 3, use this function to make your <iframe/> responsive. In this case, the ratio is used, width and height are ignored. (#13)
adds functionality for embedding Box videos, via the embed_box() function (#28)
version bump for development

updates README to show some custom formatting (#25, thanks @koncina and @ginolhac)
deprecates hms() and secs() in favor of use_start_time() (#24)
adds function embed_user2017(): embed videos from UseR!2017
version bump for development

adds rickroll_channel9(), stretches definition of rickrolling
deprecates allow_full_screen argument to embed functions in favor of allowfullscreen - this will be more consistent with each service's API
adds use_start_time() for constent interface to all embed functions
adds embed_channel9() for Microsoft videos
adds support for start-time for Vimeo (#14, thanks @karthik for tip)
adds embed_user2016()
version bump for development

Added a NEWS.md file to track changes to the package.
Added a vignette.
Added helper function secs() and query argument to both embed_vimeo() and embed_youtube().
Added functions rickroll_vimeo() and rickroll_youtube().
Added functions embed_vimeo() and embed_youtube().