Add induced kwarg in is_subgraph_isomorphic

[georgios-ts]

This commit adds a kwarg induced in is_subgraph_isomorphic to determine if we should check for a node-induced subgraph or not induced. Previously, only node-induced case was supported.
In not induced case, the changes are minimal: we shouldn't check R_new pruning rule and check neighbors in R_suc and R_pred rules only in the second graph.

[coveralls]

Pull Request Test Coverage Report for Build 967643698

• 41 of 42 (97.62%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 97.517%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/isomorphism.rs	33	34	97.06%

Totals
Change from base Build 960868250:	0.007%
Covered Lines:	8168
Relevant Lines:	8376

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💛 - Coveralls

[mtreinish]

Codewise this LGTM, it's a relatively simple change. Just a few minor docs issues then I think this is good to go.

[mtreinish]

LGTM< thanks for updating so quickly. There is one nit inline, but not worth blocking anything over.