Create a crate, relax solana dependencies in crate

[0xripleys]

1. Move core logic into sdk/ crate
2. Make solana versions flexible in sdk/
3. remove some unused deps across sdk and program

[codecov-commenter]

Codecov Report

Merging #118 (cce6556) into upcoming (9b7da68) will decrease coverage by 2.05%.
The diff coverage is 45.40%.

@@             Coverage Diff              @@
##           upcoming     #118      +/-   ##
============================================
- Coverage     81.17%   79.12%   -2.06%     
============================================
  Files            33       36       +3     
  Lines          8761     9006     +245     
============================================
+ Hits           7112     7126      +14     
- Misses         1649     1880     +231     

Impacted Files	Coverage Δ
token-lending/cli/src/lending_state.rs	0.00% <0.00%> (ø)
token-lending/program/src/lib.rs	100.00% <ø> (ø)
token-lending/program/tests/flash_borrow_repay.rs	88.72% <0.00%> (ø)
token-lending/sdk/src/instruction.rs	90.32% <ø> (ø)
token-lending/sdk/src/math/rate.rs	98.24% <ø> (ø)
token-lending/sdk/src/state/last_update.rs	78.57% <ø> (ø)
token-lending/cli/src/main.rs	0.12% <0.50%> (-0.05%)	⬇️
token-lending/sdk/src/state/obligation.rs	92.91% <50.00%> (ø)
token-lending/program/src/processor.rs	72.00% <75.00%> (+0.73%)	⬆️
token-lending/sdk/src/oracles.rs	96.55% <96.55%> (ø)
... and 14 more

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