Support multiple injections per file #8

Currently, injection marker lines are matched greedily. If a file contains more than one pair of markers, all lines between the first and last marker are replaced:

  # %%base16_template: test-1##default %%
- # %%base16_template_end%%
-
- THIS WILL BE DELETED
-
- # %%base16_template: test-2##default %%
  # %%base16_template_end%%

Unsuspecting users might be surprised by this…

If the match were non-greedy, multiple marker blocks could be replaced in a file. For example, if two templates both set environment variables (like FZF_DEFAULT_OPTS), they could be injected into the same file.