[Pull Request] Add icon Mastodon, Bluesky and Tumblr

[Vctrsnts]

First of all, thank you for this theme I discovered to use on my Hugo server.

Secondly, I noticed that the Mastodon ( mastodon-simple ), Blueskye ( bluesky-simple ) and Tumblr ( tumblr-simple ) icons weren't available, so I created a copy of the svg.toml file and added them to my server.

The code is the following:

mastodon-simple = '''
<svg role="img" viewBox="0 0 24 24" fill="currentColor" xmlns="http://www.w3.org/2000/svg"><title>Mastodon</title><path d="M23.268 5.313c-.35-2.578-2.617-4.61-5.304-5.004C17.51.242 15.792 0 11.813 0h-.03c-3.98 0-4.835.242-5.288.309C3.882.692 1.496 2,518,917 5,127.64 6,412.61 7,837,661 9,143c.074 1,874,088 3,745.26 5,611,118 1,24,325 2,47.62 3,68.55 2,237 2,777 4,098 4.96 4,857 2,336,792 4,849,923 7.256.38.265-.061.527-.132.786-.213.585-.184 1.27-.39 1.774-.753a.057.057 0 0 0 .023-.043v-1.809a.052.052 0 0 0-.02-.041.053.053 0 0 0-.046-.01 20.282 20.282 0 0 1-4.709.545c-2.73 0-3.463-1.284-3.674-1.818a5.593 5.593 0 0 1-.319-1.433.053.053 0 0 1 .066-.054c1,517,363 3,072,546 4,632,546,376 0 .75 0 1,125-.01 1.57-.044 3,224-.124 4.768-.422.038-.008.077-.015.11-.024 2.435-.464 4.753-1.92 4.989-5.604.008-.145.03-1.52.03-1.67.002-.512.167-3.63-.024-5.545zm-3.748 9.195h-2.561V8.29c0-1.309-.55-1.976-1.67-1.976-1.23 0-1.846.79-1.846 2.35v3.403h-2.546V8.663c0-1.56-.617-2.35-1.848-2.35-1.112 0-1.668.668-1.67 1.977v6.218H4.822V8.102c0-1.31.337-2.35 1.011-3.12.696-.77 1.608-1.164 2.74-1.164 1.311 0 2.302.5 2.962 1.498l.638 1.06.638-1.06c.66-.999 1.65-1.498 2.96-1.498 1.13 0 2.043.395 2.74 1.164.675.77 1.012 1.81 1.012 3.12z"/></svg>
'''
bluesky-simple = '''
<svg role="img" viewBox="0 0 24 24" fill="currentColor" xmlns="http://www.w3.org/2000/svg"><title>Bluesky</title><path d="M12 10.8c-1.087-2.114-4.046-6.053-6.798-7.995C2.566.944 1.561 1,266,902 1,565,139 1,908 0 3.08 0 3,768c0 .69,378 5,65,624 6,479,815 2,736 3,713 3.66 6,383 3.364.136-.02.275-.039.415-.056-.138.022-.276.04-.415.056-3.912.58-7.387 2.005-2.83 7.078 5.013 5.19 6.87-1.113 7,823-4,308,953 3,195 2.05 9,271 7,733 4,308 4,267-4,308 1,172-6,498-2.74-7,078a8,741 8,741 0 0 1-.415-.056c.14.017.279.036.415.056 2.67.297 5.568-.628 6.383-3.364.246-.828.624-5.79.624-6.478 0-.69-.139-1.861-.902-2.206-.659-.298-1.664-.62-4.3 1.24C16.046 4.748 13.087 8.687 12 10.8Z"/></svg>
'''
tumblr-simple = '''
<svg role="img" viewBox="0 0 24 24" fill="currentColor" xmlns="http://www.w3.org/2000/svg"><title>Tumblr</title><path d="M14.563 24c-5.093 0-7.031-3.756-7.031-6.411V9.747H5.116V6.648c3.63-1.313 4.512-4.596 4.71-6.469C9.84.051 9.941 0 9.999 0h3.517v6.114h4.801v3.633h-4.82v7.47c.016 1.001.375 2.371 2.207 2.371h.09c.631-.02 1.486-.205 1.936-.419l1.156 3.425c-.436.636-2.4 1.374-4.156 1.404h-.178l.011.002z"/></svg>
'''

It works correctly, in case you want to add it to the repository file.
I've added the mastodon-simple one, so it follows the same pattern as github, bluesky, and tumblr.

Sorry if I don't do the pull request myself, but I get lost in this stuff and I don't want to change anything that might break the code.
So I'd rather provide the code and let you make the changes.

Thanks for everything.