Changes:
- Fix potential memory bug in curl() when doubling the buffer is
insufficient.
- Added unit test for curl_echo() to post large multipart data.
- Fix IDN unit test error "string has forbidden bi-directional
properties"
The curl() and curl_download() functions provide highly configurable
drop-in replacements for base url() and download.file() with better
performance, support for encryption (https, ftps), gzip compression,
authentication, and other 'libcurl' goodies. The core of the package
implements a framework for performing fully customized requests where
data can be processed either in memory, on disk, or streaming via the
callback or connection interfaces.
