add dummy RcEntry trait for rc tree key

Dependencies

• [2] YATBB4O7 run cargo fmt
• [3] OTWDDJE7 Trait/type cleanup
• [4] WS4ZQM4R Debugging, tests, etc.
• [5] W2MIZD5B Single file databases + CRC for the root pages (checking the other pages makes everything very slow)
• [6] ECPAFJSB add env_borrow for Txn and MutTxn
• [7] 5LSYTRQ6 More docs, example, and fixing the free page diagnostic function for mutable transactions
• [8] OP6SVMOD Resetting history
• [9] YDHYZA77 Adding the RootPage trait to access the raw bytes of a root page (needed in libpijul)
• [10] YWFYZNLZ Cleanup + inter-process concurrency
• [11] KMT3MF5N Drop a database
• [12] E4MD6T3L Proofreading and commenting of this crate (massive bug fixes included)
• [13] YXKP4AIW New file locks, with multiple sets of free pages
• [14] TJ2R4HAZ Accessing the root pages (unsafely, of course)

Change contents

• replacement in "sanakirja/src/environment/muttxn.rs" at line 5
  [3.80263]→[3.2691:2750](∅→∅)
  − impl<E: Borrow<Env>, T> std::fmt::Debug for MutTxn<E, T> {
  [3.80263]

  [3.37172]
  + impl<E: Borrow<Env>, T, R: RcEntry> std::fmt::Debug for MutTxn<E, T, R> {
• edit in "sanakirja/src/environment/muttxn.rs" at line 10
  [3.37287]

  [3.37287]
  +

  + pub trait RcEntry: PartialEq + Storable {}
• replacement in "sanakirja/src/environment/muttxn.rs" at line 14
  [3.80290]→[3.59:98](∅→∅)
  − pub struct MutTxn<E: Borrow<Env>, T> {
  [3.80290]

  [3.2751]
  + pub struct MutTxn<E: Borrow<Env>, T, R: RcEntry> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 31
  [3.7288]→[3.1513:1560](∅→∅)
  − pub(crate) rc: Option<btree::Db<u64, ()>>,
  [3.7288]

  [3.7289]
  + pub(crate) rc: Option<btree::Db<R, ()>>,
• replacement in "sanakirja/src/environment/muttxn.rs" at line 53
  [3.80903]→[3.0:39](∅→∅)
  − impl<E: Borrow<Env>, T> MutTxn<E, T> {
  [3.80903]

  [2.2393]
  + impl<E: Borrow<Env>, T, R: RcEntry> MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 62
  [3.7735]→[3.99:147](∅→∅),[3.80903]→[3.99:147](∅→∅)
  − impl<E: Borrow<Env>, T> Drop for MutTxn<E, T> {
  [3.7735]

  [3.80962]
  + impl<E: Borrow<Env>, T, R: RcEntry> Drop for MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 84
  [3.8146]→[3.318:391](∅→∅),[3.81284]→[3.318:391](∅→∅)
  − impl<'a, E: Borrow<Env>, T> Commit for MutTxn<E, &'a mut MutTxn<E, T>> {
  [3.8146]

  [3.37309]
  + impl<'a, E: Borrow<Env>, T, R: RcEntry> Commit for MutTxn<E, &'a mut MutTxn<E, T, R>, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 149
  [3.82078]→[3.82078:82162](∅→∅)
  − pub fn mut_txn_begin<E: Borrow<Self>>(env: E) -> Result<MutTxn<E, ()>, Error> {
  [3.82078]

  [3.82162]
  + pub fn mut_txn_begin<E: Borrow<Self>, R: RcEntry>(env: E) -> Result<MutTxn<E, (), R>, Error> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 214
  [3.3232]→[3.809:857](∅→∅),[3.84060]→[3.809:857](∅→∅)
  − impl<E: Borrow<Env>> Commit for MutTxn<E, ()> {
  [3.3232]

  [3.84119]
  + impl<E: Borrow<Env>, R: RcEntry> Commit for MutTxn<E, (), R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 338
  [3.86004]→[3.1077:1116](∅→∅)
  − impl<E: Borrow<Env>, T> MutTxn<E, T> {
  [3.86004]

  [3.15482]
  + impl<E: Borrow<Env>, T, R: RcEntry> MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 449
  [3.87011]→[3.1117:1186](∅→∅)
  − impl<E: Borrow<Env>, T> sanakirja_core::AllocPage for MutTxn<E, T> {
  [3.87011]

  [3.87091]
  + impl<E: Borrow<Env>, T, R: RcEntry> sanakirja_core::AllocPage for MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 532
  [3.19838]→[3.19838:19877](∅→∅)
  − impl<E: Borrow<Env>, A> MutTxn<E, A> {
  [3.19838]

  [3.19877]
  + impl<E: Borrow<Env>, A, R: RcEntry> MutTxn<E, A, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 597
  [3.90733]→[3.1187:1255](∅→∅)
  − impl<E: Borrow<Env>, A> sanakirja_core::LoadPage for MutTxn<E, A> {
  [3.90733]

  [3.20953]
  + impl<E: Borrow<Env>, A, R: RcEntry> sanakirja_core::LoadPage for MutTxn<E, A, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 621
  [3.4392]→[3.68:120](∅→∅)
  − impl<E: Borrow<Env>, T> RootPage for MutTxn<E, T> {
  [3.4392]

  [3.120]
  + impl<E: Borrow<Env>, T, R: RcEntry> RootPage for MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 630
  [3.367]→[3.20978:21017](∅→∅),[3.4392]→[3.20978:21017](∅→∅)
  − impl<E: Borrow<Env>, T> MutTxn<E, T> {
  [3.367]

  [3.21017]
  + impl<E: Borrow<Env>, T, R: RcEntry> MutTxn<E, T, R> {
• replacement in "sanakirja/src/environment/muttxn.rs" at line 656
  [3.21349]→[3.21349:21399](∅→∅)
  − impl<E: Borrow<Env>, T> RootDb for MutTxn<E, T> {
  [3.21349]

  [3.21399]
  + impl<E: Borrow<Env>, T, R: RcEntry> RootDb for MutTxn<E, T, R> {