* Replaces conda_* and pip_* with pkg_index_provides
* Because this function can fail in so many ways I've added pkg_index_provides_strerror() and a detection macro PKG_INDEX_PROVIDES_FAILED() to make things easier

* test_pip_index_provides
* test_conda_provides
* test_conda_get_active_environment
* test_delivery_gather_tool_versions

Fix tests:

* global.sysconfdir duplicates the environment string
* Use delivery_free()
* Use globals_free()

* delivery_gather_tool_versions now returns non-zero if unable to determine a tool's version

* Break delivery.c into smaller components

* Continuation of #19

* Fixes always_update_base_environment override bug added by PR #19

* Finish type hinting implementation

* ini_getval_* functions now able to affect rendering mode using INI_READ_RAW and INI_READ_RENDER
* Created pointers to deeply nested structures to increase readability
* Output from ini_write() is more consistent, with fewer errant spaces and line feeds
* Fixes accidental regression in #19. INIVAL_TYPE_STR_ARRAY never produced an array of pointers to char. This needs to be corrected in the future. i.e. It has always generated a new-line delimited string, not a StrList, or array.

* Fix strlist_append_tokenize

* original pointer is no longer modified
* token strings are stripped of leading space before appending to the list

* Use defines instead of magic numbers

* delivery_init: add render_mode argument

* test_conda: Add render mode

* test_ini: Add render mode

* Only add conda packages and wheels to the image

* docker images are saved to the packages directory and will be consumed by the image if present.

* Render template variables after bootstrapping the delivery

* 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