RFR: 7903128: Overhaul jextract README [v2]

[Jorn Vernee]

On Thu, 24 Mar 2022 13:49:41 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Maurizio Cimadamore has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Simplify dir tree structure
>>  - More fixes
>
> README.md line 115:
> 
>> 113: #### Filtering symbols
>> 114: 
>> 115: The `jextract` tool includes several customization options. Users can select what in which package the generated code should be emitted, and what the name of the main extracted class should be. To allow for symbol filtering, `jextract` can generate a *dump* of all the symbols encountered in an header file; this dump can be manipulated, and then used as an argument file (using the `@argfile` syntax also available in other JDK tools) to e.g. generate bindings only for a *subset* of symbols seen by `jextract`. For instance, if we run `jextract` with as follows:
> 
> Suggestion:
> 
> The `jextract` tool includes several customization options. Users can select in which package the generated code should be emitted, and what the name of the main extracted class should be. To allow for symbol filtering, `jextract` can generate a *dump* of all the symbols encountered in an header file; this dump can be manipulated, and then used as an argument file (using the `@argfile` syntax also available in other JDK tools) to e.g. generate bindings only for a *subset* of symbols seen by `jextract`. For instance, if we run `jextract` with as follows:

I think this should also mention the corresponding command line options. i.e. `-t`, `--header-class-name`. For filtering the example below is good enough

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PR: https://git.openjdk.java.net/jextract/pull/3