Replace lz4 with lz4_flex and clickhouse-rs-cityhash-sys with cityhash-rs

[loyd]

Now, this crate is pure Rust implementation and doesn't contain any C/C++ dependencies.

lz4-flex doesn't support LZ4HC mode, so Compression::Lz4Hc is deprecated now and becomes alias to Compression::Lz4.

No significant difference in performance is detected:

group                    lz4flex                                master
-----                    -------                                ------
insert/lz4               1.00     56.1±2.14ns   951.7 MB/sec    1.00     56.3±2.01ns   947.9 MB/sec
insert/no compression    1.02     51.6±2.81ns  1035.3 MB/sec    1.00     50.6±2.56ns  1054.5 MB/sec
select/lz4               1.01     39.0±6.11ns   587.1 MB/sec    1.00     38.5±4.14ns   594.5 MB/sec
select/no compression    1.01     30.8±2.82ns   744.0 MB/sec    1.00     30.5±2.98ns   750.2 MB/sec

Closes #107.

[blind-oracle]

Are there plans for a release tag? :)

[loyd]

@blind-oracle released in v0.12.2