v0.6.0

Implemented some features for $(( ))

Support of parameters and variables

🍣 echo $(( $$ / $$ ))
1
🍣 A=100 ; echo $(( A  + $A ))
200

Support of **

🍣 A=100 ; echo $(( 2 ** 10 ))
1024
🍣 A=100 ; echo $(( 2 ** 0 ))
1
🍣 A=100 ; echo $(( 2 ** -1 ))
sush:  2 ** -1 : exponent less than 0 (error token is "-1")