Allow to exclude files/directories from the embedding

[olena-zmiiova]

In this PR, a doc-excludes configuration property was introduced for embed-code. It allows files and directories to be excluded from the code embedding by passing the glob-pattern string to it (as for doc-includes and code-includes). It can be done by a config file or a cli argument. Example of a config file:

code-path: "../../Some-Code-Snippets/src"
docs-path: "../some/docs"
doc-excludes: "**/*-old.md,**/deprecated/**.*"

[dmytro-kashcheiev]

@olena-zmiiova LGTM