There have been many improvements:

Move ordering has been vastly improved, mainly due to Counter Move heuristics, SEE, and promotions.
Search is faster due to optimizations.
Can now play the endgame better due to a few utility functions.

Match results vs. Chess 1.3:

STC 5sec + 50ms:
C:\Windows\system32>"K:\LittleBlitzer\ELO" 871 71 58
Number of games: 1000
Winning fraction: 0.9
Elo difference: +381.697
LOS: 1

VSTC 1sec + 50ms:
C:\Windows\system32>"K:\LittleBlitzer\ELO" 229 159 612
Number of games: 1000
Winning fraction: 0.535
Elo difference: +24.3603
LOS: 0.99981

LTC 30sec + 500ms:
C:\Windows\system32>"K:\LittleBlitzer\ELO" 7 9 3
Number of games: 19
Winning fraction: 0.447368
Elo difference: -36.7081
LOS: 0.308538

Many improvements:
Transposition table fully implemented.
Futility pruning.
Pawn hash table.
PVSearch.
Revamped move generation.
Revamped internal data structures.
Faster perft.

Results against Chess 1.2:

STC 5sec + 50ms:
C:\Windows\system32>"K:\LittleBlitzer\ELO" 928 1 71
Number of games: 1000
Winning fraction: 0.9635
Elo difference: +568.624
LOS: 1

VSTC 1sec + 50ms:
C:\Windows\system32>"K:\LittleBlitzer\ELO" 899 2 99
Number of games: 1000
Winning fraction: 0.9485
Elo difference: +506.092
LOS: 1

LTC 30sec + 500ms:
C:\Windows\system32>K:\LittleBlitzer\ELO 298 0 2
Number of games: 300
Winning fraction: 0.996667
Elo difference: +990.268
LOS: 1

Not so many changes in this release, mostly changes in search.
About 70 ELO stronger than Chess 1.1
Endgame knowledge, starting a transposition table, and Nalimov tablebase probing almost complete.

This version is 302 ELO stronger than Chess 1.0! The most notable changes are:

Evaluation function sped up by about 50% due to popcount
Null move pruning is fully implemented, but there are a couple of bugs with it
Better move ordering
King piece square tables
Doubled pawn penalty

More changes to come!

Huge progress! The engine sends the info to the GUI very well, can search to depth 8 or 9 and has actually beaten me in a bullet game! I would estimate the engine's strength at about 1400-1500 ELO. Let's hope the next release comes soon and makes more improvements!

There have been many, many improvements since the last release, mainly:
(1) Perft was implemented
(2) With the help of Perft, I was able to make the move generator close to perfect
(3) Switched to native C++ threads
(4) More uci friendly
(5) Many optimizations
(6) Kingside castling was implemented

Many more improvements are sure to come very soon!

Many improvements.

I have mostly stabilized the position, fen, and most other uci commands. I am putting in a large portion of my time into implementing minimax and then alpha-beta search techniques. At the moment, this is a perfectly legal uci engine! See you next release!

This work so far has taken about a month to write.