Long names for `git log -S` and `git log -G`

[Illia Bobyr <illia.bobyr@gmail.com>]

Hello,

I would like to add long names for the `-S` and `-G` options for `git log`.
It seems that most options have long versions, though there are some 
exceptions.

I was wondering if there could be any objections.
And also, what would be a good name for each.

Both are provided by the diff-pickaxe functionality.
`-S` is already affected by `--pickaxe-regex` and both `-G` and `-S` are 
affected by `--pickaxe-all`.

Also,`diffcore` docs says:

 > "-G<regular-expression>" (mnemonic: grep)

I was thinking of `--pickaxe` for `-S` and `--grep` for `-G`.
And it would probably make sense to discuss this before I try submitting 
a patch.

`--pickaxe-grep` for `-G` seems like a reasonable alternative name for `-G`.
Not sure what would be a reasonably short alternative for `-S`.
`--pickaxe-occurance-change` seems too long, and might not be as clear.
`--pickaxe-occurance-count-change` is just way too long.

Thank you,
Illia Bobyr