RFR: SKARA-1194: Implement git webrev --no-comments option

[Aleksey Shipilev]

hg webrev had a `-C` / `--no-comments` option that skipped printing the comments for each file, i.e. commit messages. GitWebrev accepts the same option, but it does not seem to be implemented. Producing a webrev for a branch with a lot of commits looks badly then.

For example, current report with `-C`:


 ------ ------ ------ ------ --- New Patch Raw doc/panama_jextract.html

    8065b5cc: 8270898: update panama_jextract.md and panama_jextract.html files
    bedc58a3: 8257892: long double not handled by jextract
    2d966367: Consolidate all the various documents in the repository.
    3dc23ea0: 8253419: jextract should generate RuntimeHelper as a package private class
    52adf7f5: updating samples for CSupport->CLinker
    33cba7a0: adding tensorflow sample
    06675b1e: updating samples. changed constants class to use package constructor
    6809ef51: Samples update after 8249879. Added opengl sample
    abb6e377: updating samples for recent MemoryAccess changes.
    ebba5406: 8248710: jextract should not generate Cstring, Cpointer, Cint C-X utility classes
    45d41d75: * Fixed include path to be OS/SDK version independent
    ...

    992 lines changed; 992 ins; 0 del; 0 mod; 0 unchg


Fixed report with `-C`:


 ------ ------ ------ ------ --- New Patch Raw doc/panama_jextract.html

    992 lines changed; 992 ins; 0 del; 0 mod; 0 unchg 


Additional testing:
 - [x] Eyeballing the reports with/without `-C`

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/skara/pull/1224/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1224&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1194
  Stats: 31 lines in 5 files changed: 15 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/skara/pull/1224.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1224/head:pull/1224

PR: https://git.openjdk.java.net/skara/pull/1224