How to discriminate valid phones and silence using nemo forced aligner
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**Is your feature request related to a problem? Please describe.**
I tried to use forced aligner to generate timestamps for my audio files, I got ctm results in tokens like this:
100001 1 0.00 0.44 \<b>
100001 1 0.44 0.04 WORD1
100001 1 0.48 0.20 \<b>
100001 1 0.68 0.04 WORD2
100001 1 0.72 0.20 \<b>
100001 1 0.92 0.04 WORD3
100001 1 0.96 0.16 \<b>
100001 1 1.12 0.04 WORD4

Every valid token(none blank ones) has the same duration 0.04, while \<b>'s duration changes. when I tried to use another model , the fixed value changed from 0.04 to 0.08, but still keeps the same for valid phones.
I believe the real duration for a valid phone varies, and some parts of the vowels were wrongly moved to \<b>, which makes it hard to discriminate valid phones and real silence part. It should be quite common that there are no noteworthy silence between words in some sentences.

**Describe the solution you'd like**

Is it possible to make the timestamp around \<b> more accurate, or add some other symbols for noteworthy silence like "sp"/"sil"? 
