Extract consts module (#282)

Extracts miscellaneous constants that were floating around in the
toplevel into their own module.

src/consts.rs

@@ -0,0 +1,20 @@
+//! Miscellaneous constant values
+
+/// YubiKey max buffer size
+pub(crate) const CB_BUF_MAX: usize = 3072;
+
+/// YubiKey max object size
+pub(crate) const CB_OBJ_MAX: usize = CB_BUF_MAX - 9;
+
+pub(crate) const CB_OBJ_TAG_MIN: usize = 2; // 1 byte tag + 1 byte len
+#[cfg(feature = "untested")]
+pub(crate) const CB_OBJ_TAG_MAX: usize = CB_OBJ_TAG_MIN + 2; // 1 byte tag + 3 bytes len
+
+// Admin tags
+pub(crate) const TAG_ADMIN_FLAGS_1: u8 = 0x81;
+pub(crate) const TAG_ADMIN_SALT: u8 = 0x82;
+pub(crate) const TAG_ADMIN_TIMESTAMP: u8 = 0x83;
+
+// Protected tags
+pub(crate) const TAG_PROTECTED_FLAGS_1: u8 = 0x81;
+pub(crate) const TAG_PROTECTED_MGM: u8 = 0x89;