Add `gemini_envinit' which initializes some parts of the structure
from the environment.
Add proxy support in the form of a `proxy' field in the structure
that can hold a host string.
Simplfy header handling in `gemini_read', removing the
`GEMINI_STRICT' flag.
Add the `-h' option to gemini-cat(1) to set the proxy host.
Remove the `-e' option from gemini-cat(1).
Add environment variable support to gemini-cat(1), including
`GEMINI_TOFU_WRITE', which will set the corresponding flag.
`gemini_open' is now `gemini_connect'
`gemini_close' is now `gemini_fini'
`gemini_connect' will try to use the `socketfd' struct member, if valid.
`gemini_read' now returns 0 whenever the response header has been read.
`gemini_read' no longer handles user-input (status 10) itself.
`gemini_connect_query' has been added so callers can handle user-input.
`libgeminiclient.c' no longer needs `readpassphrase' and `libbsd'.
styan