Change default minimal SQLite API version

From 3.6.8 to 3.14.0.
Use `old_sqlite` feature to keep 3.6.8 (or 3.7.16) as the minimal version.
Use `modern_sqlite` for SQLite API > 3.14.0.
Also remove old 3.6.23 and 3.7.7 bindings.

src/util/mod.rs

@@ -5,7 +5,7 @@ pub(crate) use param_cache::ParamIndexCache;
 pub(crate) use small_cstr::SmallCString;
 
 // Doesn't use any modern features or vtab stuff, but is only used by them.
-#[cfg(any(feature = "modern_sqlite", feature = "vtab"))]
+#[cfg(any(not(feature = "old_sqlite"), feature = "vtab"))]
 mod sqlite_string;
-#[cfg(any(feature = "modern_sqlite", feature = "vtab"))]
+#[cfg(any(not(feature = "old_sqlite"), feature = "vtab"))]
 pub(crate) use sqlite_string::SqliteMallocString;

src/util/sqlite_string.rs

@@ -2,7 +2,7 @@
 // used in each feature. Avoid having to track this for each function. We will
 // still warn for anything that's not used by either, though.
 #![cfg_attr(
-    not(all(feature = "vtab", feature = "modern-sqlite")),
+    not(all(feature = "vtab", not(feature = "old_sqlite"))),
     allow(dead_code)
 )]
 use crate::ffi;