Add statistics to parquet-schema command display

[sadikovi]

This PR adds statistics value to display for a column when running parquet-schema command with additional information display (parquet-schema /path/to/file true). Example of some prints are below:

column 0:
--------------------------------------------------------------------------------
column type: INT32
column path: "b_struct.b_c_int"
...
statistics: {min: N/A, max: N/A, distinct_count: N/A, null_count: 8, 
min_max_deprecated: true}

column 0:
--------------------------------------------------------------------------------
column type: BYTE_ARRAY
column path: "first"
...
statistics: {min: [97], max: [97], distinct_count: N/A, null_count: 0, 
min_max_deprecated: true}

column 10:
--------------------------------------------------------------------------------
column type: INT96
column path: "timestamp_col"
...
statistics: N/A

Unfortunately, statistics string can be a bit long, for example:

column 1:
--------------------------------------------------------------------------------
column type: DOUBLE
column path: "bp2"
...
dictionary page offset: 10788
statistics: {min: 69.05000000000001, max: 70.60000000000001, distinct_count: N/A, 
null_count: 0, min_max_deprecated: false}

Closes #156

[sadikovi]

@sunchao could you review this PR? Let me know if I should make any changes or add more tests. Thanks!

[coveralls]

Pull Request Test Coverage Report for Build 617

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 17 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.06%) to 95.544%

---

Files with Coverage Reduction	New Missed Lines	%
encodings/encoding.rs	1	94.77%
schema/printer.rs	6	70.52%
file/statistics.rs	10	92.71%
<!--	Total:	17		-->

Totals
Change from base Build 613:	-0.06%
Covered Lines:	12414
Relevant Lines:	12993

---

💛 - Coveralls

[sunchao]

Looks good. I'm wondering if it's better to make this optional, i.e., only print it when an extra argument such as -statistics is specified. Thought?

[sadikovi]

That is a good idea, though we would have to provide true and -statistics flags and they should work together. My understanding was that if user provided true we show everything.

Slightly off-topic: I was thinking if we should improve our CLI tools, for example, have better handling of parameters and help display like cargo --help and have different modes for parquet-schema - --short for just schema, --ext for bunch of other properties and --all for everything.

I can add just an extra option for statistics or I can extend to support different options, like I mentioned above. Let me know what you think is better - I am happy to change either way!

[sunchao]

Agree that the CLI tool needs improvement - I was also thinking that we can enable colored output as well as making the output more formatted, etc.

I think we can just re-use the true option for everything now, and leave the aforementioned improvements as a followup. :)