* Move core library sources into src/lib/core
* Move command-line programs into src/cli

* Change return value of conda_setup_headless() from void to int

* Replace exit() with return;

* Return early if unpacking the micromamba binary fails

* Exit program when pointer to INIFILE is NULL.

* Validation function cannot otherwise proceed

* The way the logic is set up I've decided to duplicate the installation code for now until I find time to revise it

* The only meaningful difference between a "fresh start" and reusing the conda installation is a rmtree().

* Exposes STASIS_DOWNLOAD_TIMEOUT environment variable

* Sets the connection timeout for libcurl to 30, instead of 300.

* Export ini_section_create() function

* Add download() tests

* Add conda_*() tests

* Add boilerplate source file for test framework

* Fixes segfault reported by @GeorgeJCleary (#10)

* The key is now an array index. When key is -1, the env variable is not defined.

* Free resources only when continue on error is disabled (#11)

* Fix segfault due to premature shutdown/cleanup

* If conda_setup_headless cannot succeed, die

* Set STASIS_SYSCONFDIR for tests

* Will return -1 on error
* Still returns HTTP code if error is server-side

* Returns HTTP status code
* Emits curl error message to stderr (or to a buffer if the third argument is not NULL)

* Fix invalid type passed to CURLOPT_FOLLOWLOCATION