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.
styan