Add v1.19 configuration options

[hf]

Specifically:

• error_if_exists
• reuse_logs
• paranoid_checks
• max_open_files

For details, see: https://github.com/google/leveldb/blob/v1.19/include/leveldb/options.h

[codecov-io]

Current coverage is 73.30% (diff: 75.00%)

Merging #8 into master will decrease coverage by 0.88%

@@             master         #8   diff @@
==========================================
  Files            19         19          
  Lines           434        457    +23   
  Methods           0          0          
  Messages          0          0          
  Branches         87         87          
==========================================
+ Hits            322        335    +13   
- Misses           82         90     +8   
- Partials         30         32     +2   

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