Give dependent packages more control over compilation

[wm75]

rust-bio/rust-htslib#185 addresses an aspect of this already, but the decision to link statically to most hts-sys dependencies is made in the hts-sys Cargo.toml itself:

hts-sys/Cargo.toml

Lines 19 to 27 in 40496b7

	[dependencies]
	libz-sys = { version = "1.1.0", default-features = false, features = ["zlib-ng", "static"] }
	bzip2-sys = { version = "0.1.8", optional = true }
	lzma-sys = { version = "0.1.16", optional = true, features = ["static"] }
	curl-sys = { version = "0.4.78", optional = true, features = ["static-curl", "static-ssl", "protocol-ftp"] }
	libdeflate-sys = { version = "1.21.0", optional = true }
	[target.'cfg(all(unix, not(target_os = "macos")))'.dependencies]
	openssl-sys = { version = "0.9.56", optional = true }

and cannot be changed from outside.

Wouldn't it be better to remove all "static" feature requests from that section?
For convenience one could add a "static-dependencies" feature to hts-sys, which would make it easy to opt into the current behavior?